Deuterium substituted positron emission tomography (PET) imaging agents and their pharmacological application

ABSTRACT

The present invention relates to deuterated compounds according to Formula I-A, Formula II-A, Formula II-D, and Formula III-A. These compounds can be used as PET imaging agents for evaluating Parkinson&#39;s Disease, Alzheimer Disease, and for determining specific serotonin reuptake inhibitor (SSRIi) activity for treatment of depression. The present invention also relates to pharmaceutical compositions comprising a pharmaceutical acceptable carrier and a compound of Formula I-A, Formulae II-A, Formula II-D, or Formula III-A, or a pharmaceutically acceptable salt thereof.

BACKGROUND OF THE INVENTION

Deuterium (D) is a stable isotope of hydrogen (H). While the differences in the physical and chemical properties between hydrogen and deuterium are relatively small (Meanwell, J. Med. Chem. 2011, 54:2529-91), deuterated compounds can have significant effects on biological and chemical processes that were developed optimally for hydrogen. The deuterium substitution is slightly less lipophilic than hydrogen, Δ log P=−0.006 and the molar volume of deuterium is smaller than hydrogen by 0.140 cm³/mol per atom. The carbon-deuterium (C-D) bonds are shorter than carbon hydrogen (C—H) bonds by 0.005 Å, therefore the activation energy for breaking a C-D vs C—H bond is significantly higher. Functionally, this reduces the cleavage rate for C-D bonds 6.7 times over C—H bonds (Kuchar, Molecules 2015, 20:16186-220), which can have a profound effect on drug pharmacokinetic properties.

Recent reports on deuterium substituted active pharmaceuticals have demonstrated benefits of the deuterium's kinetic isotope effect on the safety and clearance of drug substances and creation of new drugs through deuterated versions of existing molecules (Gant, J. Med. Chem. 2014, 57:3595-611). Some examples, such as tetrabenazine (NITOMAN or XENAZINE), deuterated tetrabenazine (SD-809, AUSTEDO), dextromethorphan, and D6-dextromethorphan (AVP-786) are shown below.

Deuterated tetrabenazine (SD-809) was recently approved by the FDA for treatment of chorea associated with Huntington's disease. Another example is AVP-786, deuterated dextromethorphan, which is designed to treat agitation in patients with Alzheimer disease (Garay, Expert Opin. Investig. Drugs 2017, 26:121-32).

The ability to moderate drug metabolism through hydrogen to deuterium substitution provides a novel approach in solving common complications of imaging agents—a lack of suitable resident time in vivo. In the past few decades there have been reports on using hydrogen to deuterium substitution to improve in vivo PET imaging agents (Kuchar, Molecules 2015, 20:16186-220; Guengerich, J Labelled Comp Radiopharm 2013, 56:428-31). A purpose of substituting deuterium for hydrogen is to slow down the in vivo metabolism to reduce the loss of radioactive tracer while maintaining binding capability for a specific enzyme or receptor binding site. One example is the use of ¹¹C-L-deprenyl-D2 (instead of ¹¹C-L-deprenyl) for mapping MAO-B enzyme (monoamine oxidase-B; amine oxygen oxidoreductase-B) activity in the brain (Fowler, J. Nucl. Med. 1995, 36:1255-62; Logan, Nucl. Med. Biol. 2000, 27:43-9).

Another example of hydrogen to deuterium substitution for developing PET tracers is the tetra-deuterated ¹⁸F-fluoro-reboxetine-D4, which improved the in vivo stability of the deuterated PET tracers by retarding in vivo metabolism (Lin, Nucl. Med. Biol. 2005, 2:415-22; Ding, Curr. Pharm. Des. 2006, 12:3831-45). In addition, ¹¹C-choline, ¹¹C-D4-choline, ¹⁸F-fluoroethyl-choline and ¹⁸F-fluoroethyl-D4-choline have been compared in patients, to study tumor metabolic activity (Beauregard, Cancer Imaging 2016, 16:41; Nitsch, J. Nucl. Med. 2016, 57:38s-42s; Smith, Nucl. Med. Biol. 2011, 38:39-51; Witney, Clin. Cancer Res. 2012, 18:1063-72).

There exists a need to develop improved PET imaging agents, for example, using hydrogen to deuterium substitution, for evaluating conditions such as Parkinson's Disease, Alzheimer Disease, and serotonin transporter binding of specific serotonin reuptake inhibitor (SSRI) for treatment of depression.

BRIEF SUMMARY OF THE INVENTION

The present disclosure provides deuterium substituted tetrabenazine derivatives labeled with ¹⁸F as PET imaging agents for diagnosis of Parkinson's disease. Non radioactive deuterated derivatives provide drugs targeting vesicular monoamine transporter 2 for therapy of movement disorders.

In one embodiment, the present disclosure provides a compound having Formula I-A:

or a pharmaceutically acceptable salt thereof, wherein: R¹ is C₁₋₄ alkyl and is optionally substituted with one or more deuterium atoms; and X is ¹⁸F or ¹⁹F; Y is —(CR^(a)R^(b))_(n)—, wherein R^(a) and R^(b) are each independently hydrogen or deuterium atoms, n is an integer from 1 to 6; provided that at least one deuterium atom is present at either R¹ or Y; and provided that when n is 2, R¹ is not CH₃.

The present disclosure also provides deuterium substituted compounds as a PET imaging agent for diagnosis of Alzheimer disease.

In one embodiment, the present disclosure provides a compound having Formula (II-A):

or a pharmaceutically acceptable salt thereof, wherein: R² is C₁₋₄ alkyl and is optionally substituted with one or more deuterium atoms; X is ¹⁸F or ¹⁹F; Y is —[O(CR^(a)R^(b))₂]_(m)—, wherein R^(a) and R^(b) are each independently hydrogen or deuterium atoms, and m is an integer from 1 to 6; and A¹, A², A³, A⁴, and A⁵ are each independently N, CH, or C and at most three of A¹, A², A³, A⁴, and A⁵ are N; provided that at least one deuterium atom is present at either R² or Y.

In another embodiment, the present disclosure provides a compound having Formula (II-D):

or a pharmaceutically acceptable salt thereof, wherein:

R³ is C₁₋₄ alkyl, wherein R³ is substituted with one or more deuterium atoms and one or more of carbon atoms of the C₁₋₄ alkyl are optionally ¹¹C;

B¹, B², B³, and B⁴ are each independently C, N, or CH, and at most two of B¹, B², B³, and B⁴ are N;

X is hydrogen, ¹⁸F, or ¹⁹F;

W is N or CH; and

Z is O, S, or NH;

provided that the compound is labeled with ¹¹C or ¹⁸F.

The present disclosure further provides deuterium substituted diaryl sulfide compounds for PET imaging of serotonin transporters in the brain.

In one embodiment, the present disclosure provides a compound having Formula (III-A):

or a pharmaceutically acceptable salt thereof, wherein:

R⁴ and R⁵ are each independently hydrogen or C₁₋₄ alkyl, wherein the C₁₋₄ alkyl is optionally substituted with one or more deuterium atoms;

X is ¹⁸F or ¹⁹F;

Y is —(CR^(a)R^(b))_(n)—, wherein R^(a) and R^(b) are each independently hydrogen or deuterium atoms, and n is an integer from 1 to 6; and

R⁶ is hydrogen, halo, or CN;

provided that at least one deuterium atom is present at R⁴, R⁵, or Y.

In one embodiment, the present disclosure relates to a pharmaceutical composition comprising a deuterium substituted compound disclosed herein and a pharmaceutically acceptable carrier.

In one embodiment, the present disclosure relates to a method for imaging in a subject, comprising administering a radiolabeled compound disclosed herein to the subject; and obtaining an image of the subject or a portion of the subject.

In one embodiment, the present disclosure relates to a method of in vivo imaging, comprising administering an effective amount of a radiolabeled compound disclosed herein to a subject and detecting the pattern of radioactivity of the compound in the subject.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure provides novel deuterium substituted PET imaging agents for evaluating Parkinson's Disease, Alzheimer Disease, and for determining specific serotonin reuptake inhibitor (SSRI) activity for treatment of depression.

As used herein, “a,” “an,” or “the” means one or more unless otherwise specified.

The term “or” can be conjunctive or disjunctive.

Open terms such as “include,” “including,” “contain,” “containing” and the like mean “comprising.”

The term “about,” as used herein, is intended to qualify the numerical values which it modifies, denoting such a value as variable within a margin of error. The term “about” should be understood to mean that range which would encompass the recited value and the range which would be included by rounding up or down to that figure as well, taking into account significant figures. The term “about” as used herein, includes the recited number ±10%. For example, “about 10” means 9 to 11.

When ranges of values are disclosed, and the notation “from n₁ . . . to n₂” or “n₁-n₂” is used, where n₁ and n₂ are the numbers, then unless otherwise specified, this notation is intended to include the numbers themselves and the range between them. This range may be integral or continuous between and including the end values.

The term “deuterium enrichment” refers to the percentage of incorporation of deuterium at a given position in a compound in the place of hydrogen. For example, deuterium enrichment of 1% at a given position means that 1% of molecules in a given sample contain deuterium at the specified position. Because the naturally occurring distribution of deuterium is about 0.0156%, deuterium enrichment at any position in a compound synthesized using non-enriched starting materials is about 0.0156%. The deuterium enrichment can be determined using conventional analytical methods known to one of ordinary skill in the art, including mass spectrometry and nuclear magnetic resonance spectroscopy.

The term “deuterium enrichment factor,” as used herein, means the ratio between the isotopic abundance and the natural abundance of deuterium. For example, a position designated as having deuterium can have a minimum isotopic enrichment factor of at least 3340 (50.1% deuterium incorporation) at each atom designated as deuterium in a compound disclosed herein.

In some embodiments, a compound of the present disclosure has an isotopic enrichment factor for each designated deuterium atom of at least 3500 (54.6% deuterium incorporation at each designated deuterium atom), at least 4000 (62.4% deuterium incorporation), at least 4500 (70.2% deuterium incorporation), at least 5000 (78% deuterium), at least 5500 (85.8% deuterium incorporation), at least 6000 (93.6% deuterium incorporation), at least 6090 (95% deuterium incorporation), at least 6218 (97% deuterium incorporation), at least 6346 (99% deuterium incorporation), or at least 6378 (99.5% deuterium incorporation).

The term “is/are deuterium,” when used to describe a given position in a compound disclosed herein or the symbol “D,” when used to represent a given position in a drawing of a compound, means that the specified position is enriched with deuterium above the naturally occurring distribution of deuterium. In some embodiments, deuterium enrichment is at least about 1%, at least about 5%, at least about 10%, at least about 20%, at least about 50%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, at least about 97%, at least about 98%, or at least about 99% of deuterium at the specified position.

The deuterated compounds disclosed herein can be prepared using commercially available deuterium-containing starting materials. Many deuterium-containing starting materials have >99% deuterium enrichment at the specified position.

Some of the compounds disclosed herein contain one or more asymmetric centers and may thus give rise to enantiomers, diastereomers, and other stereoisomeric forms. The invention is meant to encompass the compounds in all such possible forms, as well as their racemic and resolved forms and mixtures thereof.

Certain compounds disclosed herein are labeled with a radioactive fluorine atom ¹⁸F. Certain other compounds disclosed herein contain the stable isotope of fluorine, ¹⁹F, which is used interchangeably with F herein.

As used herein, the term “pharmaceutically acceptable salt” refers to those salts which are, within the scope of sound medical judgment, suitable for use in contact with the tissues of humans and lower animals without undue toxicity, irritation, allergic response and the like, and are commensurate with a reasonable benefit/risk ratio. Pharmaceutically acceptable salts are well known in the art. For example, S. M. Berge et al., describe pharmaceutically acceptable salts in detail in J. Pharmaceutical Sciences, 1977, 66, 1-19, incorporated herein by reference.

The term “pharmaceutically acceptable salts” embraces salts with inorganic and organic acids, and inorganic and organic bases. The pharmaceutically acceptable salts include, but are not limited to, metal salts such as sodium salt, potassium salt, cesium salt and the like; alkaline earth metals such as calcium salt, magnesium salt and the like; organic amine salts such as triethylamine salt, pyridine salt, picoline salt, ethanolamine salt, triethanolamine salt, dicyclohexylamine salt, N,N′-dibenzylethylenediamine salt and the like; inorganic acid salts such as hydrochloride, hydrobromide, phosphate, sulphate and the like; organic acid salts such as citrate, lactate, tartrate, maleate, fumarate, mandelate, acetate, dichloroacetate, trifluoroacetate, oxalate, formate and the like; sulfonates such as methanesulfonate, benzenesulfonate, p-toluenesulfonate and the like; and amino acid salts such as arginate, asparginate, glutamate and the like.

The term “treating” or “treatment” refers to administering a therapy in an amount, manner, or mode effective to improve a condition, symptom, or parameter associated with a disorder or to slow or prevent progression of a disorder, to either a statistically significant degree or to a degree detectable to one skilled in the art. An effective amount, manner, or mode can vary depending on the subject and may be tailored to the subject. A subject includes, but not limited to, a human or an animal.

Deuterated ¹⁸F—FP-DTBZ (¹⁸F-AV-133) as a Vesicular Monoamine Transporter 2 (VMAT2) Imaging Agent

Fluoroalkyl derivatives of dihydroxy-tetrabenazine have been prepared and tested as imaging agents for vesicular monoamine transporter 2 (VMAT2) in the brain (Goswami, Nucl. Med. Biol. 2006, 33:685-94; Kilbourn, Nucl. Med. Biol. 2007, 34:233-7). PET imaging using ¹¹C-dihydrotetrabenazine, (¹¹C-DTBZ) is useful to map the distribution VMAT2 in neurons. The ¹⁸F labeled FP-DTBZ (¹⁸F—FP-(+)-DTBZ, ¹⁸F-AV-133), with a longer physical half-life, has also been developed. In the past few years, several reports have described the clinical usefulness of ¹⁸F-AV-133 as a VMAT2 imaging agent. Results of human clinical studies for ¹⁸F-AV-133/PET have suggested that it is a useful agent in assisting diagnosis and monitoring of Parkinson's disease.

In relation to the discovery of the effects of deuterium on metabolic clearance, an additional area of use for ¹⁸F-AV-133/PET that demonstrated this effect, was in visualizing beta cells within the pancreas. It was proposed that the VMAT2 binding in the pancreas may be a useful indicator for measuring beta cell mass, which is significantly reduced in patients with diabetes (Kung, J. Nucl. Med. 2008, 49:1171-6; Raffo, J. Endocrinol. 2008, 198:41-9; Harris, J. Mol. Med. 2008, 86:5-16; Harris, Nucl. Med. Biol. 2013, 40:60-4; Freeby, Islets 2012, 4:393-7).

Both of ¹¹C-DTBZ and ¹⁸F—FP-DTBZ have been tested in humans as vesicular monoamine transporter 2 (VMAT2) imaging agents for diagnosis of Parkinson's disease. ¹⁸F—FE-DTBZ has also been investigated as a potential pancreas imaging agent.

In an effort to develop additional VMAT2 imaging agents specifically targeting beta cells, similar derivatives, ¹⁸F-fluoroethyl-DTBZ (FE-DTBZ) and the corresponding deuterated ¹⁸F-fluoroethyl-DTBZ-D4 (¹⁸F—FE-D4-DTBZ-D4), have been prepared for imaging VMAT2 in the pancreas (Eriksson, Nucl. Med. Biol. 2010, 37:357-63; Jahan, EJNMMI Res 2011, 1:33).

Of additional note to these studies, there may be side products produced during the preparation of ¹⁸F—FP-DTBZ. It is likely that one of the impurities was derived from a nucleophilic substitution of the fluoride ion that induced an elimination reaction instead. The elimination reaction likely occurred by breaking the C—H bond first, which led to the elimination reaction. Without wishing to be bound by theory, it is believed that substituting the hydrogen atoms with deuterium on the ¹⁸F propyl group can reduce the elimination reaction, and thus improve the labeling reaction (Scheme 1). In addition, the deuterium atoms on the fluoropropyl group can provide the compounds with better in vivo stability for imaging VMAT2 binding sites in the brain of Parkinson's patients.

The present disclosure provides deuterium substituted tetrabenazine derivatives as a PET imaging agent for diagnosis and therapy of Parkinson's disease.

In one embodiment, the present disclosure provides a compound having Formula I-A:

or a pharmaceutically acceptable salt thereof, wherein: R¹ is C₁₋₄ alkyl and is optionally substituted with one or more deuterium atoms; and X is ¹⁸F or ¹⁹F; Y is —(CR^(a)R^(b))_(n)—, wherein R^(a) and R^(b) are each independently hydrogen or deuterium atoms, n is an integer from 1 to 6; provided that at least one deuterium atom is present at either R¹ or Y; and provided that when n is 2, R¹ is not CH₃.

One embodiment of the present disclosure provides a compound of Formula I-A wherein n is 3, 4, 5, or 6. In some embodiments, n is 3. In some embodiments, Y is —(CH₂)₂—,

—(CD₂)₂-, —(CH₂)₃—, —(CD₂)₃-, —(CH₂)₄—, —(CD₂)₄-, —(CH₂)₅—, —(CD₂)₅-, —(CH₂)₆—, or —(CD₂)₆-. In some embodiments, Y is —(CH₂)₃— or —(CD₂)₃-.

One embodiment of the present disclosure provides a compound of Formula I-A wherein R¹ is C₁₋₄ alkyl that can be deuterated or non-deuterated. In some embodiments, R¹ is —CH₃, —CD₃, —CH₂CH₃, —CD₂CD₃, —CD₂CH₃, —CH₂CD₃, —CH(CH₃)₂, —CD(CD₃)₂,

—CH(CD₃)₂, —CD(CH₃)₂, —CH₂CH(CH₃)₂, —CD₂CH(CH₃)₂, —CH₂CD(CH₃)₂, —CH₂CH(CD₃)₂, —CD₂CD(CH₃)₂, —CD₂CH(CD₃)₂, —CH₂CD(CD₃)₂, or —CD₂CD(CD₃)₂. In some of these embodiments, R¹ is —CD₃, —CD₂CD₃, —CD₂CH₃, —CH₂CD₃, —CD(CD₃)₂,

—CH(CD₃)₂, —CD(CH₃)₂, —CD₂CH(CH₃)₂, —CH₂CD(CH₃)₂, —CH₂CH(CD₃)₂, —CD₂CD(CH₃)₂, —CD₂CH(CD₃)₂, —CH₂CD(CD₃)₂, or —CD₂CD(CD₃)₂. In some embodiments, R¹ is —CH₃ or —CD₃. In some embodiments, R¹ is —CD₃.

In some embodiments, the compound of Formula I-A has the following formula:

or a pharmaceutically acceptable salt thereof, wherein X, Y, and R¹ are as defined herein.

In some embodiments, the compound of Formula I-A has the following formula:

or a pharmaceutically acceptable salt thereof, wherein X is ¹⁸F or ¹⁹F.

In some embodiments, the compound of Formula I-A has the following formula:

or a pharmaceutically acceptable salt thereof, wherein X is ¹⁸F or ¹⁹F.

In one embodiment, the compound of Formula I-A is:

or a pharmaceutically acceptable salt thereof.

In one embodiment, the compound of Formula I-A is:

or a pharmaceutically acceptable salt thereof.

In one embodiment, the compound of Formula I-A is:

or a pharmaceutically acceptable salt thereof.

In one embodiment, the compound of Formula I-A is:

or a pharmaceutically acceptable salt thereof.

The present disclosure provides a method for diagnosing Parkinson's disease in a subject in need thereof comprising administering an effective amount of a compound of Formula I-A or a pharmaceutically acceptable salt thereof to the subject and obtaining an image of the subject or a portion of the subject. In some embodiments, the method for diagnosing Parkinson's disease comprising administering an effective amount of a compound of Formula I-A disclosed herein wherein X is ¹⁸F.

The present disclosure also provides a method for treating Parkinson's disease in a subject in need thereof comprising administering a therapeutically effective amount of a compound of Formula I-A or a pharmaceutically acceptable salt thereof to the subject. In some embodiments, the method for treating Parkinson's disease in a subject in need thereof comprising administering a therapeutically effective amount of a compound of Formula I-A disclosed herein wherein X is ¹⁹F.

Certain compounds disclosed herein may possess useful VMAT2 inhibiting activity, and may be used in the treatment or prophylaxis of a disorder in which VMAT2 plays an active role. Certain embodiments provide methods for inhibiting VMAT2. Other embodiments provide methods for treating a VMAT2-mediated disorder in a subject in need of such treatment, comprising administering to the subject a therapeutically effective amount of a compound of Formula I-A. Also provided is the use of certain compounds disclosed herein in the manufacture of a medicament for the treatment of a disorder ameliorated by the inhibition of VMAT2.

The term “VMAT2-mediated disorder” refers to a disorder that is characterized by abnormal VMAT2 activity. A VMAT2-mediated disorder may be completely or partially mediated by modulating VMAT2. In particular, a VMAT2-mediated disorder is one in which inhibition of VMAT2 results in some effect on the underlying disorder.

VMAT2-mediated disorders, include, but are not limited to, chronic hyperkinetic movement disorders, and/or any disorder which can lessened, alleviated, or prevented by administering a VMAT2 inhibitor. The term “chronic hyperkinetic movement disorders” refers to disorders characterized by non-purposeful, repetitive, disordered motor acts, variously termed “compulsive”, “rhythmical”, or “stereotyped.” In humans, chronic hyperkinetic movement disorders can be psychogenic (e.g., tics), idiopathic (as in, e.g., Tourette's syndrome and Parkinson's disease, genetic (as in, e.g., the chorea characteristic of Huntington's Disease), infectious (as in, e.g., Sydenham's Chorea), or, as in tardive dyskinesia, drug-induced. Unless otherwise stated, “chronic hyperkinetic movement disorders” refers to and includes all psychogenic, idiopathic, genetic, and drug-induced movement disorders.

In certain embodiments, the chronic hyperkinetic movement disorder is Huntington's disease. In certain embodiments, the chronic hyperkinetic movement disorder is Parkinson's disease.

Deuterated amyloid Imaging Agents for Alzheimer Disease

In Alzheimer disease (AD) β-amyloid peptide (Aβ) aggregates are deposited in extracellular plaques typically composed of straight fibrils. These structures are also found in normal aging and are sometimes referred to as senile plaques. Aβ plaque deposition (i.e. Amyloid hypothesis) is considered the key pathophysiological event leading to AD (Gauthier, Alzheimer Dement 2016, 12:60-4; Harrison, Br. J. Psychiatry 2016, 208:1-3). Research into Aβ plaque-specific imaging agents is one of the most fascinating developments in the field of brain imaging over the past fifteen years, and has been extensively reviewed. The most well characterized PET imaging agent for Aβ plaques in the brain is ¹¹C-6-OH-BTA-1, (¹¹C—PIB) (Mathis, Semin. Nucl. Med. 2012, 42:423-32), and has been used as a tracer for imaging Aβ plaques in the brain of suspected AD patients. Many different core structures have been prepared and tested. Among the hundreds of potential ligands that show good binding to Aβ plaques, four ¹⁸F labeled tracers, suitable for commercial distribution, have been successfully tested in humans (Kung, A C S Med Chem Lett 2012, 3:265-7; Villemagne, Semin. Nucl. Med. 2017, 47:75-88), and the FDA has approved three (AMYVID, NEURACEQ, and VIZAMYL) for human Aβ imaging (Scheme 2). Another Aβ plaque imaging agent, structurally similar to flutemetamol (VIZAMYL), NAV4694, has also shown excellent in vitro binding and promising in vivo kinetics in human studies (Rowe, J. Nucl. Med. 2013, 54:880-6).

¹¹C—PIB was the first agent tested in humans, which led to the development of ¹⁸F-Vizamyl and NAV4694. Additionally, modifying ¹¹C—SB-13 led to the discovery of stilbene and the styrylpyridine series of agents. Three units of polyethylene glycol chains were attached to the core. The polyethylene glycol chains are useful for adjusting the lipophilicity and providing a suitable position for fluorine substitution. All of these PET imaging agents contain an N-methyl group attached to a phenyl ring. The electron donating N-methyl anilinyl group plays an important role in binding the target sites in the Aβ plaques. Without wishing to be bound by theory, it is believed that substituting the N-methyl group with a deuterated N-methyl group can reduce the N-demethylation reaction in vivo.

Previous reports on in vivo metabolism of ¹⁸F-AV-45 (AMYVID) showed a rapid change in the plasma after intravenous (i.v.) injection. In vivo metabolism of ¹⁸F-AV-45 in mice showed that, at 30 min after an intravenous injection, only 30% of the parent ¹⁸F-AV-45 remained in the plasma. The biologic T_(1/2) of ¹⁸F-AV-45 in mouse plasma was estimated to be less than 30 min. Metabolite profiling and identification of the metabolites were done by HPLC with radioactive detection and liquid chromatography/mass spectroscopy analysis. One of the plasma metabolites was N-demethylated ¹⁸F-AV-160, which constituted about 48% of the metabolites at 30 min after injection (Scheme 3). The brain uptake of ¹⁸F-AV-160 at 2 min after injection was 4.5% ID/g of tissue, and decreased to 1.8% ID/g at 60 min. The initial uptake of the parent ¹⁸F-AV-45 was 1.5-fold higher than this metabolite. No significant binding to Aβ plaques was observed with the metabolites using AD brain-section autoradiography and the in vitro AD brain homogenate binding assay. The inhibition constant of AV-160 (K_(i)=54±5 nM) indicates at least a 20-fold reduction of binding affinity to Aβ plaques in AD brain tissue homogenates, as compared with that of the nonradioactive version of ¹⁸F-AV-45 (K_(i)=2.87±0.17 nM) (Choi, J. Nucl. Med. 2009, 50:1887-94).

In humans, the in vivo metabolism was found to be similar to that in mice (Wong, J. Nucl. Med. 2010, 51:913-20). After an injection of ¹⁸F-AV-45, the total radioactivity in plasma and the fraction of plasma radioactivity accounted for by ¹⁸F-AV-45 were rapidly reduced. Plasma radioactivity was decreased by approximately 80% within 10 min and by approximately 90% within 20 min of the injection. In addition to the parent compound, ¹⁸F-AV-45, three metabolite peaks were observed in human plasma. One of the major peaks was matched to cold reference as desmethyl-¹⁸F-AV-45 (N-desmethyl ¹⁸F-AV-45, i.e., ¹⁸F-AV-160). In comparison, ¹⁸F-AV-1 (NUERACEQ) also displayed a rapid in vivo metabolism; one of the major metabolites in human plasma was the N-desmethyl ¹⁸F-AV-1 (see Scheme 3). It is believed that the N-demethylation leads to reduced binding affinities towards Aβ plaques in the brain, and contributes to increased non-specific binding. Therefore, a novel strategy to reduce the in vivo production of ¹⁸F-AV-160 by slowing the N-demethylation process by substituting a deuterated N-methyl group on AV-45, should improve imaging by increased uptake of ¹⁸F-AV-45 to Aβ plaques in the brain and a decrease of non-specific binding (Scheme 4).

The inventors have discovered that the in vivo stability of the N-methyl-aniline group is enhanced by substitution of deuterated methyl groups for both AV-45 and AV-1. The deuterated agent, ¹⁸F-AV-45-D3 showed excellent brain uptake comparable to that observed to ¹⁸F-AV-45 after an i.v. injection in mice.

The present disclosure provides deuterium substituted compounds as a PET imaging agent for diagnosis of Alzheimer disease.

In one embodiment, the present disclosure provides a compound having Formula II-A:

or a pharmaceutically acceptable salt thereof, wherein: R² is C₁₋₄ alkyl and is optionally substituted with one or more deuterium atoms; X is ¹⁸F or F; Y is —[O(CR^(a)R^(b))₂]_(m)—, wherein R^(a) and R^(b) are each independently hydrogen or deuterium atoms, and m is an integer from 1 to 6; and A¹, A², A³, A⁴, and A⁵ are each independently N, CH, or C and at most three of A¹, A², A³, A⁴, and A⁵ are N; provided that at least one deuterium atom is present at either R² or Y.

One embodiment of the present disclosure provides a compound of Formula II-A wherein R² is C₁₋₄ alkyl that can be deuterated or non-deuterated. In some embodiments, R² is —CH₃, —CD₃, —CH₂CH₃, —CD₂CD₃, —CD₂CH₃, —CH₂CD₃, —CH(CH₃)₂, —CD(CD₃)₂,

—CH(CD₃)₂, —CD(CH₃)₂, —CH₂CH(CH₃)₂, —CD₂CH(CH₃)₂, —CH₂CD(CH₃)₂, —CH₂CH(CD₃)₂, —CD₂CD(CH₃)₂, —CD₂CH(CD₃)₂, —CH₂CD(CD₃)₂, or —CD₂CD(CD₃)₂. In some of these embodiments, R² is —CD₃, —CD₂CD₃, —CD₂CH₃, —CH₂CD₃, —CD(CD₃)₂,

—CH(CD₃)₂, —CD(CH₃)₂, —CD₂CH(CH₃)₂, —CH₂CD(CH₃)₂, —CH₂CH(CD₃)₂, —CD₂CD(CH₃)₂, —CD₂CH(CD₃)₂, —CH₂CD(CD₃)₂, or —CD₂CD(CD₃)₂. In some embodiments, R² is —CH₃ or —CD₃. In some embodiments, R² is —CD₃.

One embodiment of the present disclosure provides a compound of Formula II-A wherein m is 1, 2, 3, or 4. In one embodiment, m is 3. In some embodiments, Y is —[OCH₂CH₂]_(m)— or —[OCD₂CD₂]_(m)-. In some embodiments, Y is —[OCH₂CH₂]₃— or —[OCD₂CD₂]₃-. In some embodiments, Y is —[OCD₂CD₂]₃-.

In some embodiments, the present disclosure provides a compound of Formula II-A having the following formulae:

or a pharmaceutically acceptable salt thereof, wherein R², X, and Y are as defined herein.

In some embodiments, the compound of Formula II-A has the following formula:

or a pharmaceutically acceptable salt thereof, wherein: R² is C₁₋₂ alkyl and is optionally substituted with one or more deuterium atoms; X is ¹⁸F or ¹⁹F; Y is —[O(CR^(a)R^(b))₂]_(m)—, wherein R^(a) and R^(b) are each independently hydrogen or deuterium atoms, and m is an integer from 1 to 4; and A¹ is N or CH; provided that at least one deuterium atom is present at either R² or Y.

In some embodiments, the compound of Formula II-A has the following formula:

or a pharmaceutically acceptable salt thereof, wherein: A¹ is N or CH; and X is ¹⁸F or ¹⁹F.

In one embodiment, the compound of Formula II-A is:

or a pharmaceutically acceptable salt thereof.

In one embodiment, the compound of Formula II-A is:

or a pharmaceutically acceptable salt thereof.

In another embodiment, the present disclosure provides a compound having Formula II-D:

or a pharmaceutically acceptable salt thereof, wherein:

R³ is C₁₋₄ alkyl, wherein R³ is substituted with one or more deuterium atoms and one or more of carbon atoms of the C₁₋₄ alkyl are optionally ¹¹C;

B¹, B², B³, and B⁴ are each independently C, N, or CH, and at most two of B¹, B², B³, and B⁴ are N;

X is hydrogen, ¹⁸F, or ¹⁹F;

W is N or CH; and

Z is O, S, or NH;

provided that the compound is labeled with ¹¹C or ¹⁸F.

One embodiment of the present disclosure provides a compound of Formula II-D wherein R³ is C₁₋₄ alkyl that can be deuterated or non-deuterated. In some embodiments, R³ is

—CH₃, —CD₃, —CH₂CH₃, —CD₂CD₃, —CD₂CH₃, —CH₂CD₃, —CH(CH₃)₂, —CD(CD₃)₂, —CH(CD₃)₂, —CD(CH₃)₂, —CH₂CH(CH₃)₂, —CD₂CH(CH₃)₂, —CH₂CD(CH₃)₂, —CH₂CH(CD₃)₂, —CD₂CD(CH₃)₂, —CD₂CH(CD₃)₂, —CH₂CD(CD₃)₂, or —CD₂CD(CD₃)₂. In some of these embodiments, R³ is —CD₃, —CD₂CD₃, —CD₂CH₃, CH₂CD₃, —CD(CD₃)₂, —CH(CD₃)₂, —CD(CH₃)₂, —CD₂CH(CH₃)₂, —CH₂CD(CH₃)₂, —CH₂CH(CD₃)₂, —CD₂CD(CH₃)₂, —CD₂CH(CD₃)₂, —CH₂CD(CD₃)₂, or —CD₂CD(CD₃)₂. In some embodiments, R³ is —CH₃ or —CD₃. In some embodiments, R³ is —CD₃.

In some embodiments, the present disclosure provides a compound of Formula II-D having the following formulae:

In some other embodiments, the present disclosure provides a compound of Formula II-D having the following formulae:

In some embodiments, the compound of Formula II-D has the following formula:

or a pharmaceutically acceptable salt thereof, wherein: R³ is C₁₋₂ alkyl; B¹ is C, N, or CH; and X, W, and Z are as defined herein.

In some embodiments, the present disclosure provides a compound having Formula II-D or II-E wherein R³ is methyl substituted with one or more deuterium atoms. In some embodiments, R³ is CD₃ and X is ¹⁸F.

In some embodiments, the present disclosure provides a compound having Formula II-D or II-E wherein R³ is C₁₋₄ alkyl and one carbon atom of the C₁₋₄ alkyl is ¹¹C. In some embodiments, R³ is ¹¹CD₃ and X is hydrogen.

In some embodiments, the compound of Formula II-D has the following formula:

or a pharmaceutically acceptable salt thereof, wherein R³ and X are as defined herein. In some embodiments, R³ is —CD₃ and X is ¹⁸F. In some embodiments, R³ is —¹¹CD₃ and X is H.

In some embodiments, the compound of Formula II-D has the following formula:

or a pharmaceutically acceptable salt thereof, wherein R³ and X are as defined herein. In some embodiments, R³ is —CD₃ and X is ¹⁸F. In some embodiments, R³ is —¹¹CD₃ and X is H.

In one embodiment, the compound of Formula II-D is:

or a pharmaceutically acceptable salt thereof.

In one embodiment, the compound of Formula II-D is:

or a pharmaceutically acceptable salt thereof.

In one embodiment, the compound of Formula II-D is:

or a pharmaceutically acceptable salt thereof.

In one embodiment, the compound of Formula II-D is:

or a pharmaceutically acceptable salt thereof.

The present disclosure provides a method for diagnosing Alzheimer disease in a subject in need thereof comprising administering an effective amount of a compound of Formula II-A or a pharmaceutically acceptable salt thereof to the subject and obtaining an image of the subject or a portion of the subject. In some embodiments, the method for diagnosing Alzheimer disease comprising administering an effective amount of a compound of Formula II-A disclosed herein wherein X is ¹⁸F.

The present disclosure provides a method for diagnosing Alzheimer disease in a subject in need thereof comprising administering an effective amount of a compound of Formula II-D or a pharmaceutically acceptable salt thereof to the subject and obtaining an image of the subject or a portion of the subject. In some embodiments, the method for diagnosing Alzheimer disease comprising administering an effective amount of a compound of Formula II-D disclosed herein wherein X is ¹⁸F. In some embodiments, the method for diagnosing Alzheimer disease comprising administering an effective amount of a compound of Formula II-D disclosed herein wherein R³ is ¹¹CD₃.

Deuterated FPBM as Serotonin Transporter (SERT) Imaging Agents

Serotonin neurons in the central nervous system play an important role in normal brain function. Serotonin transporters (SERT) localized on serotonin neurons serve as the main re-uptake mechanism for terminating the action of serotonin by transporting serotonin, the neurotransmitter, from the synapse back into the presynaptic neuron. These transporters are important for controlling serotonin concentration in the synapse and its binding to the postsynaptic serotonin receptors. Selective serotonin reuptake inhibitors (SSRIs), such as Fluoxetine, Sertraline, Paroxetine, Escitalopram, specifically target SERT and prevent serotonin reuptake to the neurons. Consequently, SSRIs are useful in the treatment of depression as well as many other psychiatric conditions by controlling the concentration of serotonin in the synapse (Bousman, B M C Psychiatry 2017, 17:60). They are generally considered as the first-line therapy for depression, and they are one of the most commonly prescribed classes of drugs in the world. Positron emission tomography (PET) imaging with a suitably ¹⁸F labeled SERT inhibitor is useful as a method for probing pathophysiological and therapeutic mechanisms in various psychological diseases (Spies, Lancet Psychiatry 2015, 2:743-55). A number of SERT ligands for in vivo imaging have been developed (see structures below). ¹¹C-McN5652 was the first SERT PET imaging tracer used in humans. Development of ¹⁸F—FMe-(+)-McN5652, an S-¹⁸F-fluoromethyl analogue of (+)-McN5652, showed favorable features for SERT imaging with PET in humans (Hesse, J. Nucl. Med. Mol. Imaging 2012, 39:1001-11). PET imaging is also suitable for in vivo quantification of SERT.

Ligands with a core structure of bisphenylthiol also showed promising results as in vivo SERT imaging agents. The most commonly used SERT PET imaging agent is ¹¹C-DASB (Wilson, J. Med. Chem. 2000, 43:3103-10; Wilson, Nucl. Med. Biol. 2002, 29:509-15). It showed excellent selectivity, high reproducibility, and simple kinetic modeling for quantification (Kupers, Neuroimage 2011, 54:1336-43; Ginovart, Synapse 2004, 52:89-99). However, ¹¹C-DASB is a ¹¹C-labeled radiotracer that is limited by a short physical half-life (20 min), which is unsuitable for widespread clinical application. ¹⁸F has a longer half-life (110 min) and can be produced in several curies of activity by a cyclotron. This makes it feasible to radiolabel at a radiopharmacy and distribute the ligand regionally. Thus, an ¹⁸F-labeled SERT imaging agent may be valuable for commercial delivery via radiopharmacies. Significant efforts have been made to develop such ¹⁸F-labeled radiotracers for SERT imaging. One promising ¹⁸F-labeled ligand is ¹⁸F-4-FADAM (Huang, Eur. J. Nucl. Med. Mol. Imaging 2013, 40:115-24; Shiue, J. Nucl. Med. 2003, 44:1890-7).

Results from the first human study of ¹⁸F-4-FADAM showed that it was safe and effective for mapping SERT regional binding sites (Huang, Eur. J. Nucl. Med. Mol. Imaging 2013, 40:115-24). The regional specific uptake in the human brain correlated well with the known distribution of SERT. The optimal imaging time (about 120 min) was slightly long, but acceptable for routine clinical use. An alternative bisphenylthiol derivative, ¹⁸F—FPBM, with a different substitution on the phenyl ring has been shown to possess high selective binding (K_(i)=0.38 nM), high brain uptake (0.99% dose/g at 2 min post iv injection), and an excellent in vivo target-to-non-target ratio (7.7 at 120 min post injection) (Wang, Nucl. Med. Biol. 2008, 35:447-58; Wang, J. Nucl. Med. 2009, 50:1509-17; Wang, Nucl. Med. Biol. 2010, 37:479-86). Previously, the labeling of this diarylsulfide was performed by a nucleophilic fluorination with K¹⁸F—F/K_(2.2.2) via TsO-precursor (Scheme 5) (Qiao, Nucl. Med. Biol. 2016, 43:470-7; Zhu, Nucl. Med. Biol. 2013, 40:974-9). The desired product, ¹⁸F—FPBM, was further purified by either high-performance liquid chromatography (HPLC) or solid phase extraction (SPE). During the labeling procedure it was observed that an elimination reaction led to the production of a vinyl side product.

Similar to that observed for ¹⁸F—FP-DTBZ (¹⁸F-AV-133), the elimination reaction may occur by breaking the C—H bond first. Without wishing to be bound by theory, it is believed that substituting the hydrogen atoms on the propyl group with deuterium can reduce the eliminating reaction, thus improving the labeling reaction. In addition, N,N-dimethyl groups can be replaced by two deuterated methyl groups, which will resist the in vivo demethylation reaction.

The present disclosure provides deuterium substituted diaryl sulfide compounds for PET imaging of serotonin transporters in the brain.

In one embodiment, the present disclosure provides a compound having Formula III-A:

or a pharmaceutically acceptable salt thereof, wherein:

R⁴ and R⁵ are each independently hydrogen or C₁₋₄ alkyl, wherein the C₁₋₄ alkyl is optionally substituted with one or more deuterium atoms;

X is ¹⁸F or ¹⁹F;

Y is —(CR^(a)R^(b))_(n)—, wherein R^(a) and R^(b) are each independently hydrogen or deuterium atoms, and n is an integer from 1 to 6; and

R⁶ is hydrogen, halo, or CN;

provided that at least one deuterium atom is present at R⁴, R⁵, or Y.

One embodiment of the present disclosure provides a compound of Formula III-A wherein R⁴ and R⁵ are each independently hydrogen or C₁₋₄ alkyl that can be deuterated or non-deuterated. In some embodiments, R⁴ and R⁵ are each independently hydrogen, —CH₃, —CD₃, —CH₂CH₃, —CD₂CD₃, —CD₂CH₃, —CH₂CD₃, —CH(CH₃)₂, —CD(CD₃)₂, —CH(CD₃)₂,

—CD(CH₃)₂, —CH₂CH(CH₃)₂, —CD₂CH(CH₃)₂, —CH₂CD(CH₃)₂, —CH₂CH(CD₃)₂, —CD₂CD(CH₃)₂, —CD₂CH(CD₃)₂, —CH₂CD(CD₃)₂, or —CD₂CD(CD₃)₂. In some of these embodiments, R⁴ and R⁵ are each independently hydrogen, —CD₃, —CD₂CD₃, —CD₂CH₃, —CH₂CD₃, —CD(CD₃)₂, —CH(CD₃)₂, —CD(CH₃)₂, —CD₂CH(CH₃)₂, —CH₂CD(CH₃)₂, —CH₂CH(CD₃)₂, —CD₂CD(CH₃)₂, —CD₂CH(CD₃)₂, —CH₂CD(CD₃)₂, or —CD₂CD(CD₃)₂. In some embodiments, R⁴ and R⁵ are each independently hydrogen, —CH₃, or —CD₃. In some embodiments, both R⁴ and R⁵ are —CD₃.

One embodiment of the present disclosure provides a compound of Formula III-A wherein n is 3, 4, 5, or 6. In some embodiments, n is 3. In some embodiments, Y is —(CH₂)₂—,

—(CD₂)₂-, —(CH₂)₃—, —(CD₂)₃-, —(CH₂)₄—, —(CD₂)₄-, —(CH₂)₅—, —(CD₂)₅-, —(CH₂)₆—, or —(CD₂)₆-. In some embodiments, Y is —(CH₂)₃— or —(CD₂)₃-.

One embodiment of the present disclosure provides a compound of Formula III-A wherein R⁶ is hydrogen, F, Cl, Br, I, or CN. In some embodiments, R⁶ is hydrogen. In some embodiments, R⁶ is F, Cl, Br, or I.

In some embodiments, the compound of Formula III-A has the following formula:

or a pharmaceutically acceptable salt thereof, wherein: X is ¹⁸F or ¹⁹F; and R⁶ is hydrogen or halo.

In some embodiments, the compound of Formula III-A has the following formulae:

or a pharmaceutically acceptable salt thereof, wherein X and R⁶ are as defined herein.

In one embodiment, the compound of Formula III-A is

or a pharmaceutically acceptable salt thereof.

The present disclosure provides a method for imaging serotonin transporters in a subject in need thereof comprising administering an effective amount of a compound of Formula III-A or a pharmaceutically acceptable salt thereof to the subject and obtaining an image of the subject or a portion of the subject. In some embodiments, the method for imaging serotonin transporters comprising administering an effective amount of a compound of Formula III-A disclosed herein wherein X is ¹⁸F.

In some embodiments, the present disclosure provides a method for determining SSRI activity for treatment of depression in a subject in need thereof comprising administering an effective amount of a compound of Formula III-A disclosed herein to the subject and obtaining an image of the subject or a portion of the subject.

EXAMPLES Example 1 Synthesis of Compound Ia

Synthesis of Compound Ia-2: (2R,3R,11R)-3-Isobutyl-10-methoxy-2,3,4,6,7,11b-hexahydro-1H-pyrido[2,1-a]isoquinoline-2,9-diol

A mixture of 9-benzyl protected DTBZ (Ia-1, 380 mg, 0.96 mmol) and 10% dry Pd/C (15 mg) was stirred in THF (10 mL) and EtOH (5 mL) under H₂ at room temperature for 6 h. The reaction mixture was filtered and washed with EtOH (10 mL) and THF (10 mL). The solvent was removed under vacuum to give Ia-2 (255 mg, 87%) as a yellow solid. ¹HNMR (400 MHz, CDCl₃) δ 6.68 (s, 1H), 6.67 (s, 1H), 3.87 (s, 3H), 3.44-3.38 (m, 1H), 3.16-2.97 (m, 4H), 2.66-2.56 (m, 2H), 2.49-2.42 (m, 1H), 1.99 (t, J=2.01 Hz, 1H), 1.79-1.68 (m, 2H), 1.57-1.45 (m, 3H), 1.12-1.05 (m, 1H), 0.97-0.93 (m, 6H). HRMS calcd. for C₁₈H₂₇NO₃ [M+H]⁺ 306.2069. found 306.2100.

Synthesis of Compound Ia-4: [1,1,2,2,3,3-D6]-Propane-1,3-diylbis(4-methylbenzenesulfonate)

To a solution of compound Ia-3 (270 mg, 3.29 mmol) (99 atom % D) in THF (10 mL) was added NaOH (527 mg, 13.17 mmol) in H₂O (5 mL) at 0° C. The reaction mixture was stirred at room temperature for 1 h. TsCl (1.88 g, 9.88 mmol) in THF (10 mL) was then added dropwise. The reaction was stirred at room temperature for 24 h. H₂O (20 mL) was added and the mixture was extracted with ethyl acetate (3×30 mL). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (Ethyl Acetate (EA)/Hexane, 0% to 60%, vol/vol) to give [1,1,2,2,3,3-D6]-propane-1,3-diylbis(4-methylbenzenesulfonate), Ia-4, (970 mg, 76%) as a white solid. ¹HNMR (400 MHz, CDCl₃) δ 7.78-7.76 (m, 4H), 7.38-7.36 (m, 4H), 2.483 (s, 6H), HRMS calcd. for C₁₇H₁₄D₆O₆S₂ [M+H]⁺ 391.1156. found 391.1140.

Synthesis of Compound Ia-5: 3-(((2R,3R,11R)-2-Hydroxy-3-isobutyl-10-methoxy-2,3,4,6,7,11b-hexahydro-1H-pyrido[2,1-a]isoquinolin-9-yl)oxy)propyl-[1,1,2,2,3,3-D6])-4-methylbenzenesulfonate

A mixture of Ia-2 (44 mg, 0.14 mmol) and K₂CO₃ (119 mg, 0.86 mmol) was stirred in DMF (4 mL) at room temperature for 1 h. Compound Ia-4 (68 mg, 0.17 mmol) was then added and the reaction mixture was stirred for 24 h at room temperature. Water (5 mL) was added, and the mixture was extracted with ethyl acetate (5×15 mL). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (MeOH/DCM, 0% to 10%, vol/vol) to give Ia-5 (33.7 mg, 45%) as a light yellow solid. ¹HNMR (400 MHz, CDCl₃) δ 7.80-7.78 (m, 2H), 7.30-7.29 (m, 2H), 6.68 (s, 1H), 6.54 (s, 1H), 3.78 (s, 3H), 3.43-3.39 (m, 1H), 3.15-2.97 (m, 4H), 2.65-2.57 (m, 2H), 2.50-2.44 (m, 1H), 2.43 (s, 3H), 2.00 (t, J=2.01 Hz, 1H), 1.78-1.68 (m, 2H), 1.64-1.47 (m, 3H), 1.12-1.05 (m, 1H), 0.98-0.94 (m, 6H). HRMS calcd. for C₂₈H₃₃D₆NO₆S [M+H]⁺ 524.2953. found 524.2963.

Synthesis of compound Ia: (2R,3R,11R)-9-(3-Fluoropropoxy-[1,1,2,2,3,3-D₆])-3-isobutyl-10-methoxy-2,3,4,6,7,11b-hexahydro-1H-pyrido[2,1-a]isoquinolin-2-ol

A mixture of compound Ia-5 (30 mg, 0.06 mmol) and 1M TBAF in THF (0.17 mL, 0.17 mmol) was stirred in anhydrous THF (5 mL) at 60° C. for 5 h. H₂O (5 mL) was added, and the mixture was extracted with ethyl acetate (5×10 mL). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (MeOH/DCM, 0% to 10%, vol/vol) to give Ia (11.2 mg, 26%) as a light yellow solid. ¹HNMR (400 MHz, CDCl₃) δ 6.71 (s, 1H), 6.64 (s, 1H), 3.84 (s, 3H), 3.44-3.38 (m, 1H), 3.16-2.98 (m, 4H), 2.66-2.57 (m, 2H), 2.51-2.44 (m, 1H), 2.00 (t, J=2.01 Hz, 1H), 1.79-1.68 (m, 2H), 1.56-1.47 (m, 3H), 1.12-1.05 (m, 1H), 0.97-0.94 (m, 6H). HRMS calcd. for C₂₁H₂₆D₆FNO₃ [M+H]⁺ 372.2821. found 372.2824.

Preparation of ¹⁸F-Ia (¹⁸F-AV-133-D6) by radiolabeling was accomplished by the following steps. ¹⁸F fluoride was loaded on an activated QMA light cartridge and eluted with 0.7 mL K₂₂₂/K₂CO₃ solution (40 mg K₂CO₃, 220 mg K₂₂₂, 3.6 mL water, 18.4 mL ACN) into conical vial. The solution was dried under a flow of argon at 80° C. and azeotropically dried twice with 1 mL acetonitrile. 1 mg Ia-5 was dissolved in 0.5 ml DMSO (anhydrous) and added to dried [¹⁸F]F⁻/K₂₂₂/K₂CO₃ complex. The reaction mixture was heated for 15 min at 115° C. The resulting reaction mixture was cooled to room temperature and added to 8 mL water. The mixture was loaded onto an Oasis HLB (3 cc) cartridge. Eluted and washed twice with 3 mL water. The desired ¹⁸F-Ia was eluted with 1 ml acetonitrile (yield: 62%, RCP ˜98% HPLC (Supelco Ascentis 150×4.6 mm, ACN/10 mM ammonium format buffer (AFB) 45/55, 1 mL/min). To this solution was added about 1 mL of 10 mM AFB and injected onto prep HPLC (Phenomenex Gemini 250×10 mm, ACN/10 mM AFB 45/55, 3 mL/min). The eluent of the desired ¹⁸F-Ia was collected (660 μCi mCi, retention time 14-15 min). The solution was mixed with 18 mL water and added onto an Oasis HLB 3 cc. The activity was eluted with 1 mL 100% ethanol (590 μCi). Solution was concentrated to about 200 μL volume diluted with 1.8 mL buffer. HPLC profile on HPLC (HPLC: Supelco Ascentis 150×4.6 mm, ACN/10 mM AFB 45/55, 1 mL/min) showed single peak at 6 minutes for 18F-Ia (¹⁸F-AV-133-D6), RCY 48% (dc): RCP: 99%; SA˜182 Ci/mmol (measured at 280 nm). The retention time corresponded to cold Ia.

Example 2 In Vitro Binding Assay for Ki Determination AV-133 vs AV-133-D6 (Ia)

Tissue homogenates of striatum (dissected from rat brain) were prepared in 50 mM of HEPES, pH 7.5, and 0.3 M of sucrose. Compounds were examined for their ability to compete for the binding of ¹⁸F-AV-133 or ¹⁸F-AV-133-D6 (¹⁸F-Ia) (0.15-0.2 nM) at concentrations ranging from 10⁻⁷ to 10⁻¹² M. The binding assays were performed in glass tubes (12×75 mm) in a final volume of 0.25 mL. The nonspecific binding was defined with 10 μM (±)-tetrabenazine (TBZ). After incubation for 90 min at room temperature, the bound ligand was separated from the free ligand by filtration through glass fiber filters. The filters were washed three times with 4 mL of ice-cold PBS buffer, pH 7.4 and the radioactivity on the filters was counted with a gamma counter (WIZARD², Perkin-Elmer). Data were analyzed using the nonlinear least-square curve fitting program LIGAND to determine IC₅₀ and K_(i) was calculated by Cheng-Prusoff equation using 0.11 nM as Kd of AV-133 and AV-133-D6 (Ia).

TABLE la Comparison of in vitro binding affinity (Ki, nM) to vesicular monoamine transporter 2 (VMAT2) for (±)TBZ, AV-133, and AV-133-D6 (Ia)

(+/−)-tetrabenazine (+/−)-TBZ

FP-DTBZ AV-133

AV-133-D6 Ia Ki of cold competing drug (nM, Avg ± SD, n = 3) Hot ligand (±)TBZ AV-133 Ia (AV-133-D6) ¹⁸F-AV-133-D6 1.65 ± 0.07 0.26 ± 0.03 0.33 ± 0.06 ¹⁸F-AV-133 1.49 ± 0.24 0.33 ± 0.02 0.32 ± 0.07

The (±)TBZ showed a lower binding affinity comparable to reported in the literature. Results of binding studies for AV-133 and AV-133-D6 (Ia) showed that hydrogen to deuterium substitution provided the same binding affinity to the VMAT2 binding sites. The results showed that ¹⁸F-AV-133-D6 (Ia) is an excellent PET imaging agent for VMAT2 binding sites. Similar to the recently approved deuterated tetrabenazine SD-809, the “cold” AV-133-D6 (Ia) which shows a higher binding affinity to the target sites (VMAT2), may be a useful therapeutic agent for movement disorders.

Example 3 Comparison of FP-DTBZ Biodistribution Data in Rats

Three rats per group were used for each biodistribution study. While under isoflurane anesthesia, 0.2 mL of a saline solution containing 20 μCi of radioactive tracer was injected into the femoral vein. The rats were sacrificed at the time indicated by cardiac excision while under isoflurane anesthesia. Organs of interest were removed and weighed, and the radioactivity was counted. The percent dose per organ was calculated by comparing the tissue counts to counts of 1% of the initial dose (100 times diluted aliquots of the injected material) measured at the same time. Regional brain distribution in rats was measured after an iv injection of the radioactive tracer. Samples from different brain regions (cortex, striatum, hippocampus, cerebellum and hypothalamus) were dissected, weighed and counted. The percentage dose/g of each sample was calculated by comparing sample counts with the counts of the diluted initial dose described above. The ratio was calculated by dividing the percentage dose/g of each region by that of the cerebellum. The cerebellum was used as the reference region for calculating the ratio of target to non-target binding, because only a trace amount of VMAT2 binding site is present in the cerebellum.

TABLE 1b Biodistribution in normal male CD rats after an IV injection of ¹⁸F- FP-(+)DTBZ(average of 3 rats ± SD) % dose/g 2 min 60 min 120 min Blood 0.24 ± 0.03 0.12 ± 0.00 0.07 ± 0.01 Heart 0.96 ± 0.08 0.22 ± 0.03 0.16 ± 0.01 Muscle 0.11 ± 0.02 0.10 ± 0.01 0.07 ± 0.00 Lung 1.03 ± 0.03 0.41 ± 0.03 0.31 ± 0.02 Kidney 2.66 ± 0.15 0.63 ± 0.05 0.45 ± 0.02 Spleen 1.19 ± 0.10 0.50 ± 0.04 0.37 ± 0.05 Pancreas 2.29 ± 0.36 4.48 ± 0.27 3.56 ± 0.42 Liver 2.28 ± 0.04 2.59 ± 0.21 2.12 ± 0.20 Skin 0.19 ± 0.03 0.24 ± 0.03 0.17 ± 0.01 Brain 0.83 ± 0.06 0.35 ± 0.03 0.26 ± 0.03 Bone 0.45 ± 0.03 1.13 ± 0.07 1.86 ± 0.24 Regional Brain Distribution (% dose/gram ± SD) for ¹⁸F-FP-(+)DTBZ 2 min 60 min 120 min Cerebellum 0.68 ± 0.06 0.19 ± 0.02 0.13 ± 0.01 Striatum 1.12 ± 0.04 1.04 ± 0.05 0.87 ± 0.12 Hippocampus 0.80 ± 0.07 0.30 ± 0.01 0.24 ± 0.03 Cortex 0.82 ± 0.07 0.21 ± 0.01 0.15 ± 0.02 Remainder 0.83 ± 0.06 0.31 ± 0.02 0.21 ± 0.02 Hypothalamus 1.06 ± 0.10 0.73 ± 0.11 0.54 ± 0.11 Ratio vs. Cerebellum for ¹⁸F-FP-(+)DTBZ 2 min 60 min 120 min Cerebellum 1.00 ± 0.00 1.00 ± 0.00 1.00 ± 0.00 Striatum 1.66 ± 0.15 5.66 ± 0.72 6.54 ± 0.59 Hippocampus 1.19 ± 0.03 1.64 ± 0.19 1.79 ± 0.12 Cortex 1.21 ± 0.04 1.13 ± 0.09 1.11 ± 0.09 Remainder 1.23 ± 0.03 1.68 ± 0.07 1.59 ± 0.09 Hypothalamus 1.57 ± 0.04 3.91 ± 0.37 4.04 ± 0.66

TABLE 1c Biodistribution in normal male CD IGS rats after an IV injection of ¹⁸F- FP-(+)DTBZ-D6 (¹⁸F-Ia) (average of 3 rats ± SD) % dose/g 2 min 60 min 120 min Blood 0.23 ± 0.03 0.11 ± 0.01 0.10 ± 0.00 Heart 0.69 ± 0.12 0.26 ± 0.01 0.21 ± 0.01 Muscle 0.17 ± 0.02 0.11 ± 0.00 0.09 ± 0.01 Lung 0.87 ± 0.05 0.49 ± 0.00 0.41 ± 0.01 Kidney 1.89 ± 0.07 0.66 ± 0.04 0.59 ± 0.02 Spleen 1.04 ± 0.10 0.66 ± 0.03 0.51 ± 0.03 Pancreas 2.62 ± 0.15 5.01 ± 0.69 4.49 ± 0.17 Liver 2.79 ± 0.12 3.19 ± 0.46 3.10 ± 0.49 Skin 0.24 ± 0.02 0.25 ± 0.01 0.21 ± 0.01 Brain 0.64 ± 0.07 0.44 ± 0.02 0.34 ± 0.02 Bone 0.33 ± 0.04 0.47 ± 0.02 0.65 ± 0.03 Regional Brain Distribution (% dose/gram ± SD) for ¹⁸F-FP-(+)DTBZ- D6 (¹⁸F-Ia) 2 min 60 min 120 min Cerebellum 0.48 ± 0.04 0.23 ± 0.01 0.18 ± 0.01 Striatum 1.00 ± 0.22 1.40 ± 0.06 1.00 ± 0.08 Hippocampus 0.60 ± 0.07 0.39 ± 0.01 0.31 ± 0.04 Cortex 0.65 ± 0.07 0.26 ± 0.01 0.20 ± 0.00 Remainder 0.64 ± 0.07 0.37 ± 0.02 0.28 ± 0.02 Hypothalamus 0.82 ± 0.10 0.91 ± 0.03 0.65 ± 0.11 Ratio vs. Cerebellum for ¹⁸F-FP-(+)DTBZ-D6 (¹⁸F-Ia) 2 min 60 min 120 min Cerebellum 1.00 ± 0.00 1.00 ± 0.00 1.00 ± 0.00 Striatum 2.08 ± 0.30 6.05 ± 0.43 5.49 ± 0.43 Hippocampus 1.26 ± 0.04 1.68 ± 0.12 1.74 ± 0.32 Cortex 1.36 ± 0.05 1.13 ± 0.02 1.10 ± 0.09 Remainder 1.33 ± 0.03 1.59 ± 0.04 1.52 ± 0.03 Hypothalamus 1.71 ± 0.10 3.93 ± 0.15 3.56 ± 0.49

This comparison biodistribution study in rats between ¹⁸F—FP-(+)DTBZ and ¹⁸F—FP-DTBZ-D6 (¹⁸F-Ia) demonstrated that there was good similarity. However, the most noticeable difference is the bone uptake. The deuterated ¹⁸F—FP-DTBZ-D6 (¹⁸F-Ia) showed a clearly distinctive lowering of the bone uptake, the bone uptake at 60 and 120 min were 1.33 and 1.86% dose/g for ¹⁸F—FP-(+)DTBZ, while the deuterated ¹⁸F—FP-DTBZ-D6 (¹⁸F-Ia) showed bone uptake of 0.47 and 0.65% dose/g, respectively. The improvement shown in lowering the bone uptake is likely associated with the higher bond energy of C-D as compared to C—H; as a consequence it reduces the level of free ¹⁸F fluoride in the blood circulation.

One other major observation is the improved brain uptake at 120 min after iv injection. The total brain uptake were 0.26 vs 0.34% dose/g for ¹⁸F—FP-(+)DTBZ and ¹⁸F—FP-DTBZ-D6 (¹⁸F-Ia), respectively. This amounts to a 40% increase in total brain uptake. The two agents showed comparable regional brain uptake ratios; at 60 min post i.v. injection the striatum/cerebellum ratios were 5.66 vs 6.05 for ¹⁸F—FP-(+)DTBZ and ¹⁸F—FP-DTBZ-D6 (¹⁸F-Ia), respectively.

The hydrogen to deuterium substitution presents a clear beneficial effect on improving the in vivo pharmacokinetics of the imaging agents targeting VMAT2 in the brain; as such, the novel new chemical entity with deuterium substitution provides a better specific target binding and regional brain signal for PET imaging of VMAT2 in the brain.

The hydrogen to deuterium substitution of ¹⁸F—FP-DTBZ to ¹⁸F—FP-DTBZ-D6 clearly reduced the rate of in vivo metabolism and improved the in vivo pharmacokinetics.

The novel new chemical entity with deuterium substitution provides a better specific target binding and regional brain signal for PET imaging of VMAT2 in the brain.

Example 4 Synthesis of Compounds IIa1 and ¹⁸F-IIa1

To a solution of p-(tert-Butoxycarbonylamino)styrene, IIa-11, (2.19 g, 10 mmol) in 15 mL of DMF, 60% NaH dispersion in mineral oil (60%, 600 mg, 15 mmol) was added slowly. After stirring at room temperature for 0.5 h, deuterated iodomethane (1.46 g, 20 mmol) (99.5 atom % D) was added. The reaction was stirred at room temperature for 2 h, and the reaction mixture was quenched with 40 mL saturated ammonium chloride (NH₄Cl) at 0° C. The mixture was then extracted with 60 mL of EtOAc. The organic layer was washed with H₂O as well as brine (40 mL), dried by Na₂SO₄, and filtered. The filtrate was concentrated, and the residue was purified by flash chromatography (FC) (EtOAc/hexane=2/8) to give colorless oil, IIa-12, (2.2 g, 96.1%). ¹HNMR (400 MHz, CDCl₃) δ: 7.33-7.26 (m, 2H), 7.17-7.07 (m, 2H), 6.67-6.60 (m, 1H), 5.68-5.64 (m, 1H), 5.18-5.16 (m, 1H), 1.44 (s, 9H). ¹³CNMR (100 MHz, CDCl₃) δ: 154.49, 143.28, 136.14, 129.11, 126.28, 125.55, 112.13, 28.27. HRMS calcd. for C₁₄H₁₆D₃NO₂ 236.1604, found 237.2107[M+H]⁺.

A solution of IIa-12 (1 g, 4.1 mmol), 2-[2-[2-[(5-iodo-2-pyridinyl)oxy]ethoxy]ethoxy]ethanol (1.47 g, 4.1 mmol), potassium carbonate (0.69 g, 5.0 mmol), tetrabutylammonium bromide (1.29 g, 4.0 mmol), and palladium acetate (22 mg, 0.10 mmol) in 15 mL of DMF was deoxygenated by purging with nitrogen for 15 min and then heated at 65° C. for 2 h. The solution was cooled to room temperature (RT), diluted with 80 mL of ethyl acetate, and washed with brine (20 mL). The organic layer was dried by Na₂SO₄ and filtered. The filtrate was concentrated, and the residue was purified by FC (EtOAc/hexane=8/2) to give white solid, IIa-13, (1.27 g, 65.2%). ¹HNMR (400 MHz, CDCl₃) δ: 168.04 (d, J=2.0 Hz, 1H), 7.85 (s, 1H), 7.65-7.62 (m, 1H), 7.31-7.29 (m, 2H), 7.10-7.08 (m, 2H), 6.82 (s, 2H), 6.67-6.64 (m, 1H), 4.37-4.36 (m, 2H), 3.73 (t, J=2.0 Hz, 2H), 3.59-3.55 (m, 6H), 3.49-3.47 (m, 2H), 1.34 (s, 9H). ¹³CNMR (100 MHz, CDCl₃) δ: 162.90, 162.43, 154.46, 145.50, 142.97, 135.78, 133.96, 127.16, 126.13, 126.33, 125.77, 124.30, 111.26, 80.23, 72.53, 70.53, 70.24, 69.54, 65.11, 61.45, 28.23. HRMS calcd. for C₂₅H₃₁D₃N₂O₆ 461.2605. Found 462.2801[M+H]⁺.

A solution of IIa-13 (1 g, 2.1 mmol) in 20 mL DCM at 0° C., 2 mL Et₃N, TsCl (1.64 g, 8.7 mmol) and 10 mg DMAP were added sequentially, the reaction was stirred at 0° C. for 0.5 h, then at room temperature for overnight. The solution was washed by brine (20 mL). The organic layer was dried by Na₂SO₄ and filtered. The filtrate was concentrated, and the residue was purified by FC to give light yellow oil, IIa-14, (1.24 g, 93.2%). ¹HNMR (400 MHz, CDCl₃) δ: 8.04 (d, J=2.4 Hz, 1H), 7.81-7.77 (m, 3H), 7.44 (dd, J=1.6, 1.6 Hz, 2H), 7.11 (dd, J=1.6, 1.6 Hz 2H), 7.23 (d, J=8.8 Hz, 2H), 6.96 (d, J=2.4 Hz, 2H), 6.79 (d, J=8.8 Hz, 1H), 4.48-4.46 (m, 2H), 4.17-4.15 (m, 2H), 3.83-3.81 (m, 2H), 3.70-3.60 (m, 6H), 2.43 (s, 3H), 1.47 (s, 9H). ¹³CNMR (100 MHz, CDCl₃) δ: 163.05, 154.63, 145.62, 144.76, 143.14, 135.37, 134.07, 133.04, 1333.04, 129.80, 127.96, 127.32, 126.75, 126.43, 125.42, 124.44, 111.41, 80.40, 77.40, 77.08, 76.77, 70.76, 70.62, 69.75, 69.25, 68.71, 65.22, 28.34, 21.61. HRMS calcd. for C₃₂H₃₇D₃N₂O₈S, 615.2694. Found 616.3120[M+H]⁺.

A solution of IIa-14 (0.1 g, 0.16 mmol) and tetrabutylammonium fluoride (0.25 mL, 1.0 M in THF) in 1.5 mL of THF was stirred at 70° C. for 4 h. The reaction was evaporated in vacuum, and the residue was purified by FC to give white solid, IIa-15, (64 mg, 85.4%). ¹HNMR (400 MHz, CDCl₃) δ: 8.19 (d, J=2.0 Hz, 1H), 7.81-7.79 (m, 1H), 7.46-7.44 (m, 2H), 7.28-7.23 (m, 2H), 6.98 (d, J=2.0 Hz, 2H), 6.79 (d, J=8.4 Hz, 1H), 4.63 (d, J=4.0 Hz, 1H), 4.53-4.50 (m, 3H), 3.90-3.87 (m, 2H), 3.83-3.72 (m, 6H), 1.48 (s, 9H). ¹³CNMR (100 MHz, CDCl₃) δ: 163.10, 154.65, 145.64, 143.15, 135.33, 134.10, 127.30, 126.73, 126.42, 125.44, 124.49, 111.42, 83.99, 82.31, 80.42, 77.33, 77.01, 76.10, 70.85, 70.73, 70.55, 70.35, 69.79, 65.27, 28.47. HRMS calcd. for C₂₅H₃₀D₃FN₂O₅, 463.2562, found 464.2408[M+H]⁺.

A solution of IIa-15 (30 mg, 0.06 mmol) and 1 mL TFA was stirred at room temperature for 10 min. The reaction was evaporated in vacuo, and the residue was purified by FC to give white solid, IIa-1, (19 mg, 81.5%). ¹HNMR (400 MHz, CDCl₃) δ: 8.51 (s, 1H), 8.23 (d, J=2.0 Hz, 1H), 8.01 (dd, J=2.4, 2.4 Hz, 1H), 7.65 (dd, J=1.6, 1.6 Hz, 2H), 7.31 (dd, J=1.6, 1.6 Hz, 2H), 7.15 (d, J=3.2 Hz, 2H), 6.85 (d, J=8.4 Hz, 1H), 4.59 (t, J=4.0 Hz, 1H), 4.47-4.45 (m, 3H), 3.88-3.86 (m, 2H), 3.78-3.86 (m, 2H), 3.78-3.09 (m, 6H). ¹³CNMR (100 MHz, CDCl₃) δ: 162.87, 145.37, 141.13, 135.78, 135.72, 127.21, 127.04, 126.78, 124.74, 122.18, 110.84, 83.94, 81.83, 70.28, 69.79, 65.22. HRMS calcd. for C₂₀H₂₂D₃FN₂O₃, 363.2038; found 364.2176[M+H]⁺.

Radiolabeling AV-45-D₃ (¹⁸F-IIa-1)

Preparation of ¹⁸F-IIa1 by radiolabeling was accomplished through the following steps, which was very similar to that reported previously (Choi, J. Nucl. Med. 2009; 50:1887-94). ¹⁸F fluoride was loaded on an activated QMA light cartridge and eluted with 0.7 mL K₂₂₂/K₂CO₃ solution (40 mg K₂CO₃, 220 mg K₂₂₂, 3.6 mL water, 18.4 mL ACN) into conical vial. The solution was dried under a flow of argon at 90° C. and azeotropically dried twice with 1 mL acetonitrile. 1 mg IIa-14 was dissolved in 0.5 ml DMSO (anhydrous) and added to dried F⁻/K₂₂₂/K₂CO₃ complex. The reaction mixture was heated for 15 min at 110° C. The resulting reaction mixture was allowed to cool and 250 μL 10% HCl was added. The mixture was heated for 10 minutes at 100° C., then cooled in an icebath. The mixture was diluted with 8 mL water, neutralized with 850 μL 1 N NaOH and loaded onto a Oasis HLB (3 cc) cartridge. Mixture was eluted and washed twice with 3 mL water. The desired ¹⁸F-IIa1 was eluted with 1 ml acetonitrile (yield: 80%, RCP ˜98% HPLC (Supelco Ascentis 150×4.6 mm, ACN/10 mM ammonium format buffer (AFB) 60/40, 1 mL/min). To this solution was added about 1 mL of 10 mM AFB and injected onto prep HPLC (Phenomenex Gemini 250×10 mm, ACN/10 mM AFB 60/40, 4 mL/min). The eluent of the desired ¹⁸F-IIa1 was collected (3.37 mCi, retention time 9-10 min). The solution was mixed with 18 mL water and added onto a Oasis HLB 3 cc. The activity was eluted with 1 mL ethanol/5 μL 10% HCl (3.03 mCi). Solution was concentrated to about 200 μL volume diluted with 1.8 mL buffer. HPLC profile on HPLC (HPLC: Supelco Ascentis 150×4.6 mm, ACN/10 mM AFB 6/4, 1 mL/min) showed single peak at 6 minutes. Dose: 3.03 mCi; RCY 71% (dc): RCP: 99%; SA ˜830 Ci/mmol (measured at 350 nm). The retention time corresponded to the “cold” IIa1.

Example 5 Synthesis of Compound IIa2

A solution of 4-stilbenol (1 g, 4.7 mmol) in 40 mL THF, then Di-tert-butyl dicarbonate (4.13 g, 18.9 mmol) and Et₃N (1.91 g, 18.9 mmol) was added. The solution was stirred at 40° C. for overnight. The reaction was evaporated in vacuo, and the residue was purified by FC to give white solid, IIa-21, (1.69 g, 86.8%) ¹HNMR (400 MHz, CDCl₃) δ: 7.49-7.46 (m, 2H), 7.43-7.41 (m, 2H), 7.37 (d, J=8.8 Hz, 2H), 7.17 (dd, J=1.6, 1.6 Hz, 1H), 6.99 (s, 1H), 6.69 (s, 1H), 1.59 (s, 9H), 1.55 (s, 9H). ¹³CNMR (100 MHz, CDCl₃) δ: 152.67, 151.85, 150.25, 137.99, 135.25, 132.01, 128.39, 127.17, 127.15, 126.21, 121.45, 118.61, 83.54, 80.57, 28.37, 27.72. HRMS calcd. for C₂₄H₂₉NO₅, 411.2046. Found 412.3102 [M+H]⁺.

To a suspension of IIa-21 (1 g, 2.4 mmol) in 15 mL of DMF, 60% NaH dispersion in mineral oil (60%, 240 mg, 6 mmol) was added slowly, After stirring at room temperature for 0.5 h, deuterated iodomethane (0.73 g, 5 mmol) (≥99.5 atom % D) was added. The reaction was stirred at room temperature for 1 h, the reaction mixture was quenched with 40 mL saturated ammonium chloride (NH₄Cl) at 0° C. The mixture was then extracted with 60 mL of EtOAc. The organic layer was washed with water as well as brine (40 mL), dried by Na₂SO₄, and filtered. The filtrate was concentrated, and the residue was purified by FC (EtOAc/hexane=3/7) to give colorless oil, IIa-22, (1 g, 96.8%). ¹HNMR (400 MHz, CDCl₃) δ: 7.51 (d, J=8.8 Hz, 2H), 7.47 (d, J=8.8 Hz, 2H), 7.24 (d, J=8.4 Hz, 2H), 7.18 (d, J=8.4 Hz, 2H), 7.08 (d, J=0.8 Hz, 1H), 1.59 (s, 9H), 1.48 (s, 9H). ¹³CNMR (100 MHz, CDCl₃) δ: 151.79, 150.43, 143.20, 135.03, 134.15, 128.19, 127.40, 127.29, 126.58, 125.43, 121.47, 83.59, 80.41, 28.35, 27.21. HRMS calcd. for C₂₅H₂₈D₃NO₅, 428.2391. Found 429.3102 [M+H]⁺.

To a suspension of IIa-22 (1 g, 2.3 mmol) in 15 mL of water and 20 mL methanol, NaOH (0.46 g, 11.6 mmol) was added. The reaction was stirred at room temperature for 2 h, the reaction was neutralized with 1N HCl, extracted with ethyl acetate, dried by Na₂SO₄, and filtered. The filtrate was concentrated, and the residue was purified by FC (EtOAc/hexane=3/7) to give colorless oil, IIa-23, (0.71 g, 92.5%). ¹HNMR (400 MHz, CDCl₃) δ: 7.36 (d, J=8.4 Hz, 2H), 7.30 (d, J=8.4 Hz, 2H), 7.21 (d, J=8.4 Hz, 2H), 6.93 (dd, J=1.6, 1.6 Hz, 2H), 6.66 (d, J=7.6 Hz, 2H), 6.39 (s, 1H), 1.52 (s, 9H). ¹³CNMR (100 MHz, CDCl₃) δ: 155.95, 155.35, 142.28, 135.46, 126.51, 128.59, 127.74, 126.54, 125.87, 125.37, 115.72, 80.86, 28.42. HRMS calcd. for C₂₀H₂₀D₃NO₃, 328.1866. Found 329.1902 [M+H]⁺.

To a suspension of IIa-23 (0.7 g, 2.1 mmol) in 15 mL DMF, triethylene glycol di-p-toluenesulfonate (1.95 g, 4.2 mmol) was added, the reaction stirred at room temperature for overnight. The reaction was washed by brine, extracted by ethyl acetate, then dried by Na₂SO₄ and filtered. The filtrate was concentrated, and the residue was purified by FC (EtOAc/hexane=3/7) to give colorless oil, IIa-24, (1.18 g, 90.2%). ¹HNMR (400 MHz, CDCl₃) δ: 7.76-7.73 (m, 2H), 7.41-7.37 (m, 4H), 7.27 (dd, J=6.8, 6.8 Hz, 2H), 7.18 (d, J=8.4 Hz, 2H), 6.95-6.92 (m, 2H), 6.88-6.84 (m, 2H), 4.12 (t, J=4.8 Hz, 2H), 4.06 (t, J=4.8 Hz, 2H), 3.76 (t, J=4.8 Hz, 2H), 3.64-3.59 (m, 4H), 3.56-3.52 (m, 2H), 2.35 (s, 3H), 1.44 (s, 9H). ¹³CNMR (100 MHz, CDCl₃) δ: 158.40, 154.60, 144.79, 144.72, 134.57, 133.00, 130.21, 129.85, 127.92, 127.88, 127.65, 126.30, 125.89, 125.35, 114.84, 80.24, 70.68, 70.55, 69.69, 69.34, 69.30, 68.64, 67.44, 28.33, 21.55. HRMS calcd. for C₃₃H₃₈D₃NO₈S, 614.2741. Found 615.2736 [M+H]⁺.

A solution of IIa-24 (0.1 g, 0.16 mmol) and tetrabutylammonium fluoride (0.25 mL, 1.0 M in THF) in 1.5 mL of THF was stirred at 70° C. for 4 h. The reaction was evaporated in vacuo, and the residue was purified by FC to give white solid, IIa-25, (63 mg, 84.4%) ¹HNMR (400 MHz, CDCl₃) δ: 7.45 (dd, J=1.2, 1.2 Hz, 4H), 7.23 (d, J=8.4 Hz, 2H), 7.01-6.91 (m, 4H), 4.65-4.63 (m, 1H), 4.53-4.51 (m, 1H), 4.17 (t, J=4.4 Hz, 2H), 3.89 (t, J=4.4 Hz, 2H), 3.81-3.73 (m, 4H), 1.48 (s, 9H). ¹³CNMR (100 MHz, CDCl₃) δ: 158.51, 142.78, 134.68, 130.33, 127.98, 126.32, 126.00, 125.44, 114.87, 83.98, 82.30, 80.34, 70.90, 70.85, 70.56, 70.37, 69.82, 67.52. HRMS calcd. for C₂₆H₃₁D₃FNO₅, 462.2609. Found 407.2122 [M+H-tBu]⁺.

A solution of IIa-25 (40 mg, 0.08 mmol) and 1 mL TFA was stirred at room temperature for 10 min. The reaction was evaporated in vacuo, and the residue was purified by FC to give white solid, IIa-2, (29 mg, 92.3%). ¹HNMR (400 MHz, CDCl₃) δ: 7.41 (d, J=8.4 Hz, 2H), 7.36 (d, J=8.4 Hz, 2H), 6.90 (dd, J=5.6, 4.8 Hz, 4H), 6.61 (d, J=8.4 Hz, 2H), 4.65-4.63 (m, 1H), 4.53-4.51 (m, 1H), 4.17 (t, J=4.8 Hz, 2H), 3.90-3.88 (MHz, 2H), 3.82-3.73 (m, 6H). ¹³CNMR (100 MHz, CDCl₃) δ: 157.86, 148.77, 131.20, 127.43, 127.10, 127.05, 126.99, 124.00, 114.82, 124.00, 114.82, 112.47, 83.99, 82.31, 70.98, 70.56, 70.30, 69.85, 67.51. HRMS calcd. for C₂₁H₂₃D₃FNO₃, 362.2085. Found 363.2402 [M+H]⁺.

Example 6 Synthesis of Compound IIb

Compound IIb can be prepared by the synthetic method depicted in Scheme 9.

Example 7 Synthesis of Compound ¹¹C—PIB-D3

Compound ¹¹C—PIB-D3 can be prepared by the synthetic method depicted in Scheme 10.

Example 8 Synthesis of Compound IIc

Compound IIc can be prepared by the synthetic method depicted in Scheme 11.

Example 9 Synthesis of Compound ¹⁸F-II

Compound ¹⁸F-IIc can be prepared by the synthetic method depicted in Scheme 12.

Example 10 In Vitro Binding Assays for Aβ Aggregates of Human AD Brain Homogenates

Competitive binding assays were performed in 12×75 mm borosilicate glass tubes. The reaction mixture contained 100 μL of AD brain homogenates (20-25 ug), 100 μL of [¹⁸F]AV-45 or [¹⁸F]AV-45-D3 (˜150,000 cpm), and 100 μL of competing compounds (10⁻⁵ to 10⁻¹⁰ M diluted serially in PBS containing 0.1% bovine serum albumin) in a final volume of 0.25 mL. Nonspecific binding was defined in the presence of 1 μM of IMPY (6-iodo-2-(4′-dimethylamino-)phenyl-imidazo[1,2-a]pyridine) in the same assay tubes. The mixture was incubated for 60 min at room temperature, and the bound and the free radioactivity were separated by vacuum filtration through Whatman GF/B filters using a Brandel M-24R cell harvester, followed by washing with PBS buffer three times. The radioactivity on the filters was counted with a gamma counter (Wizard², Perkin-Elmer). Data were analyzed using the nonlinear least-square curve fitting program LIGAND to determine IC₅₀. Ki was calculated by Cheng-Prusoff equation using 3.51 nM as Kd of AV-45 and AV-45-D3.

TABLE 2a In vitro binding affinity for Aβ aggregates of human AD brain homogenates (Ki, nM) using a method described previously (Choi, 2009).

Ki of cold competing drug (nM, Avg ± SD, n = 3) Hot ligand AV-45-D3, IIa1 AV-45 AV-1-D3, IIa2 ¹⁸F-AV-45-D3 3.25 ± 0.82 3.24 ± 0.76 4.15 ± 0.75 ¹⁸F-AV-45 3.44 ± 1.22 4.02 ± 0.22 3.35 ± 0.88

Results of binding studies using either ¹⁸F-AV-45-D3 or ¹⁸F-AV-45 as the “hot ligand” showed that hydrogen to deuterium substitution (AV-45 vs AV-45-D3, AV-1-D3) exhibited the same excellent binding affinity to Aβ aggregates binding sites. All deuterated agents, AV-45-D3 (IIa1), AV-1-D3 (IIa2), displayed the same binding affinity.

Example 11 Biodistribution Study in Mice

Three mice per group were used for biodistribution study. While under isoflurane anesthesia, 0.1 mL of a saline solution containing radioactive tracer was injected into tail vein. The mice were sacrificed at the time indicated by cardiac excision while under isoflurane anesthesia. Organs of interest were removed and weighed, and the radioactivity was counted. The percent dose per organ was calculated by comparing the tissue counts to counts of 1% of the initial dose (100 times diluted aliquots of the injected material) measured at the same time.

TABLE 2b Biodistribution of ¹⁸F-AV-45-D3 (IIa1) in normal male mice. % Dose/g (Avg ± SD of n = 3) 2 min 30 min 60 min 120 min Blood 2.16 ± 0.05 2.93 ± 0.27 2.08 ± 0.07 1.36 ± 0.12 Heart 5.08 ± 0.39 2.40 ± 0.39 1.72 ± 0.19 1.18 ± 0.03 Muscle 3.21 ± 0.14 1.79 ± 0.06 1.20 ± 0.04 0.75 ± 0.07 Lung 4.88 ± 0.16 2.90 ± 0.47 1.97 ± 0.25 1.31 ± 0.03 Kidney 9.51 ± 0.80 6.41 ± 1.86 3.74 ± 0.47 2.09 ± 0.02 Spleen 2.50 ± 0.12 1.52 ± 0.21 1.22 ± 0.12 0.83 ± 0.07 Pancreas 4.94 ± 0.77 2.05 ± 0.29 1.43 ± 0.20 0.87 ± 0.15 Liver 12.0 ± 0.70 12.0 ± 0.71 8.15 ± 0.75 5.47 ± 0.29 Skin 1.24 ± 0.27 2.07 ± 0.14 1.34 ± 0.07 0.91 ± 0.13 Bone 1.74 ± 0.18 2.24 ± 0.44 2.76 ± 0.37 4.41 ± 0.77 Brain 6.26 ± 0.23 1.71 ± 0.37 1.53 ± 0.20 1.26 ± 0.04

TABLE 2c Biodistribution of ¹⁸F-AV-45 in normal male mice % Dose/g (Avg ± SD of n = 3) reported previously (Choi, 2009). 2 min 60 min 120 min 180 min Blood 2.51 ± 0.31 2.37 ± 0.27 1.96 ± 0.23 1.39 ± 0.13 Muscle 3.49 ± 0.33 1.33 ± 0.08 1.02 ± 0.07 0.78 ± 0.09 Liver 16.3 ± 5.38 11.1 ± 1.83 8.96 ± 0.28 5.39 ± 0.31 Bone 1.33 ± 0.24 3.66 ± 0.30 6.48 ± 0.34 7.83 ± 1.08 Brain 7.33 ± 1.54 1.88 ± 0.14 1.80 ± 0.20 1.48 ± 0.15

Within statistical errors the biodistribution of ¹⁸F-AV-45 and ¹⁸F-AV-45-D3 (¹⁸F-IIa1) in mice showed very similar results. Both the deuterated and none deuterated AV-45 showed comparable brain initial penetration at 2 min after an iv injection, although with a lower brain retention at later time points, 60 and 120 min.

Example 12 Synthesis of Compound FPBM (III-1)

A mixture of compound III-1-1 (50 mg, 0.18 mmol) and K₂CO₃ (76 mg, 0.55 mmol) was stirred in anhydrous DMF (3 mL) at 65° C. for 1.5 hours. Then 3-fluoropropyl-4-methylbenzenesulfonate (64 mg, 0.27 mmol) was added. The mixture was stirred for another 2 hours, cooled to room temperature and saturated solution of NaCl (12 mL) was added. The mixture was extracted with EA (15 mL×3). The organic layers were combined and dried over MgSO₄ and filtered. The filtrate was dried under vacuum, purified by flash chromatography (silica gel) (MeOH/DCM, 0% to 10%, vol/vol) to get product FPBM, III-1 (38 mg, yield 62%) as a colorless waxy material. ¹H NMR (400 MHz, Acetone) δ 7.33 (dd, J=7.7, 1.5 Hz, 1H), 7.15-7.09 (m, 1H), 6.98 (t, J=5.1 Hz, 2H), 6.79-6.74 (m, 2H), 6.63-6.59 (m, 2H), 5.26 (s, 2H), 4.69 (t, J=5.9 Hz, 1H), 4.57 (t, J=5.9 Hz, 1H), 4.09 (t, J=6.2 Hz, 2H), 3.55 (s, 2H), 2.26 (s, 6H), 2.21-2.06 (m, 2H). ¹³C NMR (100 MHz, Acetone) δ 157.53, 149.70, 139.69, 136.17, 131.11, 130.00, 127.37, 116.71, 116.25, 116.04, 114.80, 113.90, 81.36, 79.75, 63.63, 63.57, 61.88, 44.53. HRMS calcd. for C₁₈H₂₃FN₂₀S [M+H]⁺ 335.1593. Found 335.1603.

Example 13 Synthesis of Compound FPBM-D6 (III-2)

A mixture of dimethyl-d6-amine hydrochloride (0.53 g, 6.50 mmol) (99 atom % D) and Et₃N (1.32 g, 12.99 mmol) was stirred in anhydrous DCM (20 mL) at 0° C. Then compound III-2-1 (1.08 g, 4.33 mmol) in anhydrous DCM (15 mL) was added dropwise. After addition the reaction was stirred at room temperature for 5 hours. Then water (30 mL) was added and extracted with DCM (20 mL×2). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Hexane, 0% to 60%, vol/vol) to get product III-2-2 (0.95 g, yield 83%) as a colorless waxy material. ¹H NMR (400 MHz, CDCl₃) δ 7.45 (d, J=8.3 Hz, 1H), 6.83-6.79 (m, 2H), 3.81 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 159.16, 139.29, 133.52, 116.55, 112.87, 109.38, 55.59. HRMS calcd. for C₁₀H₆D₆BrNO₂ [M+H]⁺264.0506. Found 264.0529.

A mixture of compound III-2-2 (510 mg, 1.94 mmol), Cu (25 mg, 0.39 mmol), Cu₂O (27 mg, 0.19 mmol), 2-aminothiophenol (364 mg, 2.91 mmol) and Et₃N (1.96 g, 19.40 mmol) was stirred in 2-ethoxyethanol (8 mL) at 125° C. for 40 hours. The mixture was then filtered and washed with methanol (20 mL) and DCM (20 mL). The filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Hexane, 0% to 60%, vol/vol) to get product III-2-3 (370 mg, yield 62%) as a colorless stick oil. ¹H NMR (400 MHz, CDCl₃) δ 7.46 (d, J=7.6 Hz, 1H), 7.21-7.09 (m, 2H), 6.84-6.66 (m, 4H), 3.78 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 158.71, 148.65, 138.91, 136.72, 132.33, 130.62, 123.43, 118.02, 115.94, 115.80, 115.37, 111.54, 55.47. HRMS calcd. for C₁₆H₁₂D₆N₂O₂S [M+H]⁺ 309.1544. Found 309.1640.

A solution of compound III-2-3 (300 mg, 0.97 mmol) was stirred in anhydrous DCM (15 mL) at 0° C., Then 1M BBr₃ in DCM (2.92 mL, 2.92 mmol) was added drop wise under N₂. After complete addition the reaction mixture was stirred at room temperature. A saturated solution of NaHCO₃ was added and extracted with DCM (20 mL×2). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum and purified by flash chromatography (silica gel) (EA/Hexane, 0% to 80%, vol/vol) to get product III-2-4 (200 mg, yield 70%) as a colorless stick oil. ¹H NMR (400 MHz, CDCl₃) δ 7.40 (dd, J=7.6, 1.5 Hz, 1H), 7.18-7.14 (m, 1H), 6.89 (d, J=8.6 Hz, 1H), 6.73-6.54 (m, 4H), 4.44 (brs, 2H). HRMS calcd. for C₁₅H₁₀D₆N₂O₂S [M+H]⁺295.1387. Found 295.1304.

A solution of compound III-2-4 (200 mg, 0.68 mmol) was stirred in anhydrous THF (4 mL) at room temperature. Then 1M BH₃ in THF (3.4 mL, 3.40 mmol) was added. The reaction mixture was refluxed for 8 hours. When finished, the mixture was cooled and 0.5 mL concentrated HCl (0.5 mL) was cautiously added and the solvent was removed in vacuum. 10 mL of 1M HCl solution was added, then refluxed for 1 hour, cooled to room temperature and pH was adjusted to 8 with saturated solution of Na₂CO₃. The solution was extracted with EA (20 mL×3), the organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum. It was purified by flash chromatography (silica gel) (methanol/EA, 0% to 10%, vol/vol) to get product III-2-5 (135 mg, yield 71%) as a colorless waxy material. ¹H NMR (400 MHz, MeOD) δ 7.16 (dd, J=7.7, 1.5 Hz, 1H), 7.12-7.08 (m, 1H), 6.93 (d, J=8.5 Hz, 1H), 6.83 (d, J=2.7 Hz, 1H), 6.78 (dd, J=8.1, 1.3 Hz, 1H), 6.66-6.61 (m, 2H), 3.60 (s, 2H). ¹³C NMR (100 MHz, MeOD) δ 156.32, 148.33, 138.51, 134.51, 131.68, 129.18, 124.90, 117.71, 117.41, 117.33, 115.20, 115.15, 60.85. HRMS calcd. for C₁₅H₁₂D₆N₂OS [M+H]⁺ 281.1595. Found 281.1210.

A mixture of compound III-2-5 (15 mg, 0.05 mmol) and K₂CO₃ (22 mg, 0.16 mmol) was stirred in anhydrous DMF (3 mL) at 65° C. for 1.5 hours. Then 3-fluoropropyl-4-methylbenzenesulfonate (25 mg, 0.10 mmol) was added and the mixture was stirred for another 2 hours, cooled to room temperature and a saturated solution of NaCl (12 mL) was added. The mixture was extracted with EA (15 mL×3), the organic layers were combined and dried over MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (THF/Hexane, 0% to 60%, vol/vol) to get product FPBM-D6, III-2 (6 mg, yield 35%) as a colorless waxy material. ¹H NMR (400 MHz, Acetone) δ 7.33 (dd, J=7.7, 1.5 Hz, 1H), 7.15-7.10 (m, 1H), 6.98 (t, J=5.1 Hz, 2H), 6.79-6.73 (m, 2H), 6.61 (d, J=1.1 Hz, 1H), 5.24 (d, J=13.6 Hz, 2H), 4.69 (t, J=5.9 Hz, 1H), 4.57 (t, J=5.9 Hz, 1H), 4.09 (t, J=6.2 Hz, 2H), 3.55 (s, 2H), 2.26 (s, 6H), 2.21-2.08 (m, 2H). ¹³C NMR (100 MHz, Acetone) δ157.53, 149.70, 139.69, 136.17, 131.11, 130.00, 127.37, 116.71, 116.25, 116.04, 114.80, 113.90, 81.36, 79.75, 63.63, 63.57, 61.88, 44.53. HRMS calcd. for C₁₈H₁₇D₆FN₂OS [M+H]⁺ 341.1970. Found 341.1912.

Example 14 Synthesis of Compound FPBM-D12 (III-3)

To a solution of compound III-3-2 (270 mg, 3.29 mmol) (99 atom % D) in THF (10 mL) was added NaOH (527 mg, 13.17 mmol) in water (5 mL) at 0° C. The reaction mixture was stirred at room temperature for 1 hour. TsCl (1.88 g, 9.88 mmol) in THF (10 mL) was then added drop wise. The reaction was stirred at room temperature for 24 hours. H₂O (20 mL) was added and the mixture was extracted with ethyl acetate (3×30 mL). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Hexane, 0% to 60%, vol/vol) to give [1,1,2,2,3,3-D₆]-propane-1,3-diylbis(4-methylbenzenesulfonate), III-3-3, (970 mg, 76%) as a white solid. ¹HNMR (400 MHz, CDCl₃) δ 7.78-7.76 (m, 4H), 7.38-7.36 (m, 4H), 2.483 (s, 6H), HRMS calcd. for C₁₇H₁₄D₆O₆S₂ [M+H]⁺ 391.1156. Found 391.1140.

A mixture of compound III-2-6 (40 mg, 0.14 mmol) and K₂CO₃ (59 mg, 0.43 mmol) was stirred in anhydrous DMF (3 mL) at 65° C. for 1.5 hours. Then compound III-3-3 (67 mg, 0.17 mmol) was added and the mixture was stirred for another 2 h, cooled to room temperature and a saturated solution of NaCl (12 mL) was added. The mixture was extracted with EA (15 mL×3), the organic layers were combined and dried over MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (MeOH/DCM, 0% to 10%, vol/vol) to get product III-3-1 (38 mg, yield 54%) as a colorless waxy material. ¹H NMR (400 MHz, Acetone) δ 7.76 (d, J=8.2 Hz, 2H), 7.39-7.33 (m, 3H), 7.12 (t, J=7.6 Hz, 1H), 6.95 (d, J=8.6 Hz, 1H), 6.87 (d, J=2.6 Hz, 1H), 6.77 (d, J=8.0 Hz, 1H), 6.63-6.59 (m, 2H), 5.31 (s, 1H), 3.55 (s, 2H), 2.37 (s, 3H). ¹³C NMR (100 MHz, Acetone) δ 157.30, 149.78, 144.89, 139.61, 136.24, 133.20, 131.03, 130.03, 129.94, 127.69, 127.34, 116.66, 116.03, 114.80, 113.94, 61.74, 20.62. HRMS calcd. for C₂₅H₁₈D₁₂N₂O₄S₂ [M+H]+ 499.2478. Found 499.2432.

A mixture of compound III-3-1 (20 mg, 0.04 mmol) was stirred in anhydrous THF (3 mL) at 65° C. Then 1M TBAF in THF (0.2 mL, 0.20 mmol) was added, the reaction mixture was stirred for 3 h at 65° C., then the solvent was evaporated in vacuum. Water (8 mL) was added and the mixture was extracted with EA (15 mL×3). The organic layers were combined and dried over MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (THF/Hexane, 0% to 60%, vol/vol) to get product FPBM-D12, III-3 (7 mg, yield 50%) as a colorless waxy material. ¹H NMR (400 MHz, CDCl₃) δ 7.41 (dd, J=8.0, 1.6 Hz, 1H), 7.20-7.14 (m, 1H), 6.96 (d, J=8.6 Hz, 1H), 6.90 (d, J=2.8 Hz, 1H), 6.76-6.66 (m, 3H), 4.55 (brs, 1H), 3.56 (s, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 157.34, 148.29, 139.31, 136.33, 130.76, 130.08, 127.22, 118.21, 117.09, 116.39, 115.23, 114.08, 62.22. HRMS calcd. for C₁₈H₁₁D₁₂FN₂OS [M+H]⁺ 347.2347. Found 347.24.

Example 15 Synthesis of Compound FPBM-D6 (III-4-2)

A mixture of compound III-1-1 (40 mg, 0.15 mmol) and K₂CO₃ (61 mg, 0.44 mmol) was stirred in anhydrous DMF (3 mL) at 65° C. for 1.5 h. Then compound III-3-3 (68 mg, 0.18 mmol) was added and the mixture was stirred for another 2 h, cooled to room temperature and a saturated solution of NaCl (10 mL) was added. The mixture was extracted with EA (15 mL×3), the organic layers were combined and dried over MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (MeOH/DCM, 0% to 10%, vol/vol) to get product III-4-1 (45 mg, 63%) as a colorless waxy material. ¹H NMR (400 MHz, CDCl₃) δ 7.76 (d, J=8.3 Hz, 2H), 7.41 (dd, J=8.0, 1.5 Hz, 1H), 7.28-7.26 (m, 2H), 7.20-7.16 (m, 1H), 6.92 (d, J=8.6 Hz, 1H), 6.79 (d, J=2.8 Hz 1H), 6.74-6.70 (m, 2H), 6.53 (dd, J=8.6, 2.8 Hz, 1H), 4.56 (brs, 2H), 3.55 (s, 2H), 2.39 (s, 3H), 2.32 (s, 6H). ¹³C NMR (100 MHz, CDCl₃) δ 157.02, 148.36, 144.76, 139.21, 136.40, 132.86, 130.65, 130.16, 129.83, 127.84, 127.39, 118.20, 116.97, 116.18, 115.24, 114.10, 62.31, 45.33, 21.59. HRMS calcd. for C₂₅H₂₄D₆N₂O₄S₂ [M+H]⁺ 493.2102. Found 493.2013.

A mixture of compound III-4-1 (20 mg, 0.04 mmol) was stirred in anhydrous THF (5 mL) at 65° C. then 1M TBAF in THF (0.12 mL, 0.12 mmol) was added, the reaction mixture was stirred for 3 h at 65° C., then the solvent was evaporated in vacuum. Water (8 mL) was added and the mixture was extracted with EA (10 mL×3). The organic layers were combined and dried over MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (MeOH/DCM, 0% to 10%, vol/vol) to get product FPBM-D6, III-4-2 (7 mg, 51%) as a colorless waxy material. ¹H NMR (400 MHz, CDCl₃) δ 7.39 (dd, J=8.1, 1.5 Hz, 1H), 7.19-7.14 (m, 1H), 6.97 (d, J=8.6 Hz, 1H), 6.93 (d, J=2.3 Hz, 1H), 6.75-6.66 (m, 3H), 3.59 (s, 2H), 2.33 (s, 6H). HRMS calcd. for C₁₈H₁₇D₆FN₂OS [M+H]⁺ 341.1970. Found 341.2005.

Example 16 Synthesis of Compounds III-4-25 to III-4-28

A mixture of 1-bromo-2-nitrobenzene (1 g, 4.95 mmol) was stirred in concentrated H₂SO₄ (10 mL) at 0° C., NIS (1.23 g, 5.45 mmol) was added slowly. After complete addition, the reaction mixture was stirred at room temperature for 5 h, then ice water (30 mL) was added and extracted with EA (30 mL×3). The organic layers were combined and dried over MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Hexane, 0% to 15%, vol/vol) to get product III-4-3 (1.35 g, yield 84%) as a white solid. ¹H NMR (400 MHz, CDCl₃) δ 8.15 (d, J=2.0 Hz, 1H), 7.75 (dd, J=8.4, 2.0 Hz, 1H), 7.47 (d, J=8.4 Hz, 1H).

Ethanol (20 mL) was stirred at 0° C., then sodium (356 mg, 15.48 mmol) was added slowly. After all sodium was consumed and become sodium ethoxide, the solvent was warmed to 80° C., and compound III-4-4 (1.31 g, 6.19 mmol) in ethanol (10 mL) was added and the reaction mixture was stirred at 80° C. for 1 h under N₂. Then compound III-4-3 (2.63 g, 8.05 mmol) was added and refluxed for 2 h. The solvent was evaporated and H₂O (30 mL) was added, neutralized pH=5 with concentrated HCl, and extracted with EA (30 mL×3). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum and purified by flash chromatography (silica gel) (EA/Hexane, 0% to 60%, vol/vol) to get product III-4-8 (1.6 g, 57%) as a yellow solid. ¹H NMR (400 MHz, CDCl₃) δ 8.49 (d, J=1.8 Hz, 1H), 7.62 (dd, J=8.7, 1.8 Hz, 1H), 7.50 (d, J=8.6 Hz, 1H), 7.01 (dd, J=8.6, 2.6 Hz, 1H), 6.95 (d, J=2.7 Hz, 1H), 6.67 (d, J=8.7 Hz, 1H), 3.89 (s, 3H), 3.04 (s, 3H), 2.87 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 168.81, 161.87, 145.30, 145.07, 142.07, 139.17, 139.03, 133.87, 130.68, 116.97, 116.55, 112.72, 87.77, 55.68, 38.53, 34.60. HRMS calcd. for C₁₆H₁₅IN₂O₄S [M+H]+ 458.9875. Found 458.9828.

General Procedure a for the Preparation of Compound III-4-9 to III-4-12

Compounds III-4-5 to III-4-8 (2 mmol) was stirred in methanol (10 mL) at 0° C. and concentrated HCl (5 mL) was added. Then SnCl₂ (1.52 g, 8 mmol) was added and the reaction mixture was stirred at room temperature overnight. After completion the mixture was diluted with water (30 mL) and basified to pH=10 with 2M aqueous solution of NaOH, and extracted with EA (30 mL×3). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum and purified by flash chromatography (silica gel) (EA/Hexane, 0% to 80%, vol/vol) to get products III-4-9 to III-4-12 as a colorless waxy oil.

Compound III-4-9 was prepared from compound III-4-5 according to procedure A to give III-4-9 as a colorless waxy material, yield 68%. ¹H NMR (400 MHz, CDCl₃) δ 7.38 (d, J=8.1 Hz, 1H), 7.13 (d, J=8.7 Hz, 1H), 6.81 (dd, J=8.7, 2.6 Hz, 1H), 6.74 (d, J=2.6 Hz, 1H), 6.69-6.61 (m, 2H), 4.67 (s, 2H), 3.79 (s, 3H), 3.16 (s, 3H), 2.87 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 170.01, 158.97, 149.65, 139.19, 137.61, 136.33, 132.75, 122.73, 117.72, 115.92, 114.74, 114.42, 111.45, 55.49, 38.53, 34.64. HRMS calcd. for C₁₆H₁₇ClN₂O₂S [M+H]+ 337.0778. Found 337.0855.

Compound III-4-10 was prepared from compound III-4-6 according to procedure A to give III-4-10 as a colorless waxy material, yield 69%. ¹H NMR (400 MHz, CDCl₃) δ 7.30 (d, J=8.3 Hz, 1H), 7.11 (d, J=8.7 Hz, 1H), 6.87-6.74 (m, 4H), 4.76 (s, 2H), 3.79 (s, 3H), 3.17 (s, 3H), 2.88 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 170.42, 158.94, 149.66, 138.29, 137.76, 132.46, 124.61, 122.65, 120.82, 117.78, 116.17, 114.72, 111.61, 55.51, 38.63, 34.86. HRMS calcd. for C₁₆H₁₇BrN₂O₂S [M+H]⁺ 381.0272, 383.0252. Found 381.0183, 383.0162.

Compound III-4-11 was prepared from compound III-4-7 according to procedure A to give III-4-11 as a colorless waxy material, yield 71%. ¹H NMR (400 MHz, CDCl₃) δ 7.48-7.40 (m, 1H), 7.10 (d, J=8.7 Hz, 1H), 6.80 (dd, J=8.7, 2.8 Hz, 1H), 6.74 (d, J=2.8 Hz, 1H), 6.43-6.35 (m, 2H), 4.71 (s, 2H), 3.78 (s, 3H), 3.17 (s, 3H), 2.88 (s, 3H). HRMS calcd. for C₁₆H₁₇FN₂O₂S [M+H]⁺ 321.1073. Found 321.1117.

Compound III-4-12 was prepared from compound III-4-8 according to procedure A to give III-4-12 as a colorless waxy material, yield 68%. ¹H NMR (400 MHz, CDCl₃) δ 7.13 (dd, J=8.3, 6.5 Hz, 2H), 7.03 (d, J=1.5 Hz, 1H), 6.98 (dd, J=8.1, 1.6 Hz, 1H), 6.80 (dd, J=8.7, 2.6 Hz, 1H), 6.74 (d, J=2.6 Hz, 1H), 3.78 (s, 3H), 3.15 (s, 3H), 2.85 (s, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 169.98, 159.00, 149.74, 139.27, 137.74, 132.91, 126.63, 123.65, 122.46, 115.93, 111.48, 96.47, 55.50, 38.54, 34.65. HRMS calcd. for C₁₆H₁₇IN₂O₂S [M+H]⁺429.0134. Found 429.0038.

General Procedure B for the Preparation of Compound III-4-13 to III-4-16

A mixture of compound III-4-9 to III-4-12 (2 mmol) was stirred in anhydrous DCM (15 mL) at 0° C. Then 1M BBr₃ in DCM (6 mL, 6 mmol) was added drop wise under N₂. After complete addition the reaction mixture was stirred at room temperature overnight. After reaction, saturated solution of NaHCO₃ was added and the mixture was extracted with DCM (20 mL×2). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum and purified by flash chromatography (silica gel) (EA/Hexane, 0% to 80%, vol/vol) to get product III-4-13 to III-4-16 as a colorless waxy material.

Compound III-4-13 was prepared from compound III-4-9 according to procedure B to give III-4-13 as a colorless waxy material, yield 68%. ¹H NMR (400 MHz, MeOD) δ 7.27 (d, J=8.3 Hz, 1H), 7.12 (d, J=8.6 Hz, 1H), 6.78-6.76 (m, 2H), 6.65 (d, J=2.7 Hz, 1H), 6.58 (dd, J=8.3, 2.3 Hz, 1H), 3.08 (s, 3H), 2.78 (s, 3H). ¹³C NMR (100 MHz, MeOD) δ 170.69, 157.12, 150.35, 138.98, 136.85, 135.62, 132.88, 120.85, 116.81, 116.68, 114.20, 114.05, 113.12, 37.56, 33.50. HRMS calcd. for C₁₅H₁₅ClN₂O₂S [M+H]⁺ 323.0621. Found 323.0658.

Compound III-4-14 was prepared from compound III-4-10 according to procedure B to give III-4-14 as a colorless waxy material, yield 71%. ¹H NMR (400 MHz, CDCl₃) δ 7.26 (d, J=8.2 Hz, 1H), 6.87 (dd, J=7.9, 5.3 Hz, 2H), 6.80 (dd, J=8.2, 2.0 Hz, 1H), 6.64 (d, J=2.6 Hz, 1H), 6.60 (dd, J=8.6, 2.6 Hz, 1H), 3.14 (s, 3H), 2.85 (s, 3H). HRMS calcd. for C₁₅H₁₅BrN₂O₂S [M+H]⁺ 367.0116, 369.0095. Found 367.0147, 369.0127.

Compound III-4-15 was prepared from compound III-4-11 according to procedure B to give III-4-15 as a colorless waxy material, yield 69%. ¹H NMR (400 MHz, CDCl₃) δ 7.40 (dd, J=9.2, 6.4 Hz, 1H), 6.87 (d, J=8.6 Hz, 1H), 6.66 (d, J=2.6 Hz, 1H), 6.60 (dd, J=8.5, 2.4 Hz, 1H), 6.44-6.35 (m, 2H), 3.17 (s, 3H), 2.89 (s, 3H). HRMS calcd. for C₁₅H₁₅FN₂O₂S [M+H]⁺ 307.0917. Found 307.0947.

Compound III-4-16 was prepared from compound III-4-12 according to procedure B to give III-4-16 as a colorless waxy material, yield 68%. ¹H NMR (400 MHz, CDCl₃) δ 7.08 (dd, J=16.6, 4.8 Hz, 2H), 7.02-6.99 (m, 1H), 6.87 (d, J=8.6 Hz, 1H), 6.64 (d, J=2.5 Hz, 1H), 6.58 (dd, J=8.6, 2.6 Hz, 1H), 4.48 (s, 2H), 3.16 (s, 3H), 2.86 (s, 3H). HRMS calcd. for C₁₅H₁₅IN₂O₂S [M+H]⁺ 414.9977. Found 414.9912.

General Procedure C for the Preparation of Compound III-4-17 to III-4-20

Compound III-4-13 to III-4-16 (1 mmol) was stirred in anhydrous THF (5 mL) at room temperature. Then 1M BH₃ in THF (3 mL, 3 mmol) was added, the reaction mixture was refluxed for 8 h. The mixture was cooled and 0.5 mL concentrate HCl was cautiously added. The solvent was removed in vacuum, and 1M HCl solution (10 mL) was added and refluxed for 1 h, cooled to room temperature and pH was adjusted to 8 with a saturated solution of Na₂CO₃, The mixture was extracted with EA (20 mL×3), the organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum and purified by flash chromatography (silica gel) (EA/methanol, 0% to 10%, vol/vol) to get product III-4-17 to III-4-20 as a colorless waxy oil.

Compound III-4-17 was prepared from compound III-4-13 according to procedure C to give III-4-17 as a colorless waxy oil, yield 66%. ¹H NMR (400 MHz, CDCl₃) δ 7.24 (d, J=8.2 Hz, 1H), 6.87 (d, J=8.5 Hz, 1H), 6.73 (d, J=2.7 Hz, 1H), 6.70 (d, J=2.1 Hz, 1H), 6.66 (dd, J=8.2, 2.2 Hz, 1H), 6.59 (dd, J=8.5, 2.8 Hz, 1H), 3.56 (s, 2H), 2.32 (s, 6H). ¹³C NMR (100 MHz, CDCl₃) 155.25, 149.02, 138.47, 136.94, 135.69, 131.32, 125.79, 118.30, 118.04, 116.18, 115.61, 114.81, 61.60, 45.08. HRMS calcd. for C₁₅H₁₇ClN₂OS [M+H]⁺309.0828. Found 309.0780.

Compound III-4-18 was prepared from compound III-4-14 according to procedure C to give III-4-18 as a colorless waxy oil, yield 69%. ¹H NMR (400 MHz, CDCl₃) δ 7.17 (d, J=8.2 Hz, 1H), 6.91 (d, J=8.6 Hz, 1H), 6.85 (d, J=2.0 Hz, 1H), 6.83-6.77 (m, 2H), 6.62 (dd, J=8.6, 2.8 Hz, 1H), 4.79 (brs, 2H), 3.58 (s, 2H), 2.33 (s, 6H). ¹³C NMR (100 MHz, CDCl₃) δ 155.32, 149.13, 138.47, 136.98, 131.66, 125.56, 123.77, 121.13, 117.94, 117.70, 116.32, 116.16, 61.61, 45.02. HRMS calcd. for C₁₅H₁₇BrN₂OS [M+H]⁺ 353.0323, 355.0303. Found 353.0284, 355.0277.

Compound III-4-19 was prepared from compound III-4-15 according to procedure C to give III-4-19 as a colorless waxy oil, yield 63%. ¹H NMR (400 MHz, MeOD) δ 7.26 (dd, J=8.5, 6.5 Hz, 1H), 6.85 (d, J=8.5 Hz, 1H), 6.78 (d, J=2.7 Hz, 1H), 6.61 (dd, J=8.5, 2.8 Hz, 1H), 6.48 (dd, J=11.2, 2.7 Hz, 1H), 6.37-6.32 (m, 1H), 3.57 (s, 2H), 2.31 (s, 6H). 13C NMR (100 MHz, MeOD) δ 165.75, 163.33, 155.92, 151.27, 151.14, 138.01, 137.47, 137.37, 130.55, 125.54, 117.35, 115.08, 111.68, 103.76, 103.54, 100.88, 100.63, 61.20, 44.02. HRMS calcd. for C₁₅H₁₇FN₂OS [M+H]⁺ 293.1124. Found 293.0578.

Compound III-4-20 was prepared from compound III-4-16 according to procedure C to give III-4-20 as a colorless waxy oil, yield 67%. ¹H NMR (400 MHz, MeOD) δ 7.13 (d, J=1.8 Hz, 1H), 7.00 (d, J=8.5 Hz, 1H), 6.91 (dd, J=8.1, 1.8 Hz, 1H), 6.84 (dd, J=5.4, 2.7 Hz, 2H), 6.68 (dd, J=8.5, 2.7 Hz, 1H), 3.67 (s, 2H), 2.37 (s, 6H). HRMS calcd. for C₁₅H₁₇IN₂OS [M+H]⁺ 401.0185. Found 401.0158.

General Procedure D for the Preparation of Compound III-4-21 to III-4-24

Compound III-4-17 to III-4-20 (0.1 mmol) and K₂CO₃ (41 mg, 0.3 mmol) were stirred in anhydrous DMF (3 mL) at 65° C. for 1.5 h, then compound II-3-3 (39 mg, 0.1 mmol) was added and the mixture was stirred for another 2 h, cooled to room temperature and saturated solution of NaCl (10 mL) was added. The mixture was extracted with EA (15 mL×3), the organic layers were combined and dried over MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (MeOH/DCM, 0% to 10%, vol/vol) to get compound III-4-21 to III-4-24 as a colorless oil.

Compound III-4-21 was prepared from compound III-4-17 according to procedure D to give III-4-21 as a colorless oil, yield 50%. HRMS calcd. for C₂₅H₂₃D₆ClN₂O₄S₂ [M+H]⁺527.1712. Found 527.1637.

Compound III-4-22 was prepared from compound III-4-18 according to procedure D to give III-4-22 as a colorless oil, yield 51%. HRMS calcd. for C₂₅H₂₃D₆BrN₂O₄S₂ [M+H]⁺571.1207, 573.1187. Found 571.1311, 573.1288.

Compound III-4-23 was prepared from compound III-4-19 according to procedure D to give III-4-23 as a colorless oil, yield 58%. HRMS calcd. for C₂₅H₂₃D₆FN₂O₄S₂ [M+H]⁺511.2008. Found 511.1965.

Compound III-4-24 was prepared from compound III-4-20 according to procedure D to give III-4-24 as a colorless oil, yield 53%. HRMS calcd. for C₂₅H₂₃D₆IN₂O₄S₂ [M+H]⁺ 619.1068. Found 619.1003.

General Procedure E for the Preparation of Compound II-4-25 to II-4-28

Compound III-4-21 to III-4-24 (0.2 mmol) was stirred in anhydrous THF (5 mL) at 65° C. Then 1M TBAF in THF (0.6 mL, 0.6 mmol) was added. The reaction mixture was stirred for 3 h at 65° C., then the solvent was evaporated in vacuum, water (8 mL) was added. The mixture was extracted with EA (15 mL×3), the organic layers were combined and dried over MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (MeOH/DCM, 0% to 10%, vol/vol) to get product III-4-25 to III-4-28 as a colorless oil.

Compound III-4-25 was prepared from compound III-4-21 according to procedure E to give III-4-25 as a colorless oil, yield 60%. ¹H NMR (400 MHz, CDCl₃) δ 7.35 (dd, J=7.8, 0.6 Hz, 1H), 6.97 (d, J=8.6 Hz, 1H), 6.86 (d, J=2.8 Hz, 1H), 6.74-6.65 (m, 3H), 4.79 (s, 2H), 3.54 (s, 2H), 2.31 (s, 6H). ¹³C NMR (100 MHz, CDCl₃) δ 157.47 149.38, 139.36, 137.43, 135.80, 131.13, 126.85, 117.91, 116.65, 115.56, 114.66, 114.17, 62.51, 45.25. HRMS calcd. for C₁₈H₁₆D₆ClFN₂OS [M+H]⁺ 375.1580. Found 375.1649.

Compound III-4-26 was prepared used compound III-4-22 according to procedure E to give III-4-26 as a colorless oil, yield 57%. ¹H NMR (400 MHz, CDCl₃) δ 7.26 (s, 1H), 6.98 (d, J=8.6 Hz, 1H), 6.85 (dd, J=5.3, 2.4 Hz, 2H), 6.81 (dd, J=8.1, 2.1 Hz, 1H), 6.70 (dd, J=8.6, 2.9 Hz, 1H), 4.78 (s, 2H), 3.54 (s, 2H), 2.31 (s, 6H). ¹³C NMR (100 MHz, CDCl₃) δ 157.51, 149.52, 139.45, 137.53, 131.26, 126.66, 123.93, 120.79, 117.56, 116.66, 116.21, 114.17, 62.52, 45.25. HRMS calcd. for C₁₈H₁₆D₆BrFN₂OS [M+H]⁺ 419.1075, 421.1055. Found 419.1050, 421.1030.

Compound III-4-27 was prepared from compound III-4-23 according to procedure E to give III-4-27 as a colorless oil, yield 52%. ¹H NMR (400 MHz, CDCl₃) δ 7.43 (dd, J=8.2, 6.6 Hz, 1H), 6.93 (d, J=8.6 Hz, 1H), 6.85 (d, J=2.8 Hz, 1H), 6.70 (dd, J=8.6, 2.8 Hz, 1H), 6.45-6.38 (m, 2H), 4.86 (s, 2H), 3.55 (s, 2H), 2.32 (s, 6H). ¹³C NMR (100 MHz, CDCl₃) δ 165.84, 163.40, 157.25, 150.43, 150.31, 138.90, 138.54, 138.44, 130.48, 127.56, 116.63, 114.13, 112.03, 105.06, 104.84, 101.70, 101.45, 62.49, 45.25. HRMS calcd. for C₁₈H₁₆D₆F₂N₂OS [M+H]⁺ 359.1876. Found 359.1793.

Compound III-4-28 was prepared from compound III-4-24 according to procedure F to give III-4-28 as a colorless oil, yield 55%. ¹H NMR (400 MHz, MeOD) δ 7.14 (d, J=0.9 Hz, 1H), 6.99 (d, J=8.7 Hz, 1H), 6.95 (d, J=2.8 Hz, 1H), 6.92 (d, J=0.9 Hz, 2H), 6.79 (dd, J=8.7, 2.8 Hz, 1H), 3.60 (s, 2H), 2.31 (s, 6H). ¹³C NMR (100 MHz, MeOD) δ 157.92, 150.20, 138.69, 136.34, 131.21, 126.28, 125.91, 123.25, 116.58, 116.37, 114.19, 94.78, 61.17, 44.03. HRMS calcd. for C₁₈H₁₆D₆FIN₂OS [M+H]⁺ 467.0936. Found 467.0887.

Example 17 Synthesis of Compound III-5-5

A mixture of compound III-5-1 (500 mg, 2.17 mmol), Cu (28 mg, 0.43 mmol), Cu₂O (31 mg, 0.22 mmol), 2-aminothiophenol (408 mg, 3.26 mmol) and Et₃N (2.20 g, 21.74 mmol) was stirred in 2-ethoxyethanol (8 mL) at 125° C. for 40 h. The mixture was filtered and washed with methanol (20 mL) and DCM (20 mL). The filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Hexane, 0% to 60%, vol/vol) to get product III-5-2 (350 mg, yield 59%) as a white solid. ¹H NMR (400 MHz, MeOD) δ 7.36 (d, J=7.7 Hz, 1H), 7.18 (t, J=7.7 Hz, 1H), 7.07 (d, J=2.2 Hz, 1H), 6.90-6.79 (m, 3H), 6.67 (t, J=7.5 Hz, 1H), 3.79 (s, 3H). ¹³C NMR (100 MHz, MeOD) δ 172.24, 157.78, 149.77, 136.67, 136.00, 130.47, 129.60, 126.16, 117.51, 116.24, 115.11, 115.03, 112.96, 54.58. HRMS calcd. for C₁₄H₁₄N₂O₂S [M+H]⁺ 275.0854. Found 275.0821.

Compound III-5-2 (350 mg, 1.28 mmol) was stirred in anhydrous DCM (15 mL) at 0° C., then 1M BBr₃ in DCM (3.83 mL, 3.83 mmol) was added drop wise under nitrogen. After addition the reaction mixture was refluxed for 5 h, cooled and a saturated solution of NaHCO₃ was added. The mixture was extracted with a solution of DCM/MeOH (10/1) (20 mL×3). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum and purified by flash chromatography (silica gel) (EA/Hexane, 0% to 80%, vol/vol) to get product III-5-3 (230 mg, yield 69%) as a white solid. ¹H NMR (400 MHz, MeOD) δ 7.35 (d, J=7.7 Hz, 1H), 7.16 (t, J=7.7 Hz, 1H), 6.93 (d, J=2.6 Hz, 1H), 6.81 (dd, J=10.4, 8.4 Hz, 2H), 6.73-6.63 (m, 2H). ¹³C NMR (100 MHz, MeOD) δ 172.54, 155.62, 149.51, 136.76, 136.38, 130.30, 130.21, 123.93, 117.52, 117.48, 115.70, 115.11, 114.30. HRMS calcd. for C₁₃H₁₂N₂O₂S [M+H]⁺ 261.0698. Found 261.0687.

A mixture of compound III-5-3 (40 mg, 0.15 mmol) and K₂CO₃ (64 mg, 0.46 mmol) was stirred in anhydrous DMF (4 mL) at 65° C. for 1.5 h, then compound 3-fluoropropyl-4-methylbenzenesulfonate (71 mg, 0.30 mmol) was added and the mixture was stirred for another 2 h, cooled to room temperature and a saturated solution of NaCl (12 mL) was added. The mixture was extracted with EA (15 mL×3), the organic layers were combined and dried over MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Hexane, 0% to 70%, vol/vol) to get product III-5-4 (30 mg, yield 61%) as a white solid. ¹H NMR (400 MHz, CDCl₃) δ 7.41 (dd, J=7.6, 1.4 Hz, 1H), 7.25-7.18 (m, 2H), 6.96 (d, J=8.8 Hz, 1H), 6.87-6.84 (m, 1H), 6.78-6.73 (m, 2H), 4.69 (t, J=5.7 Hz, 1H), 4.57 (t, J=5.7 Hz, 1H), 4.38 (brs, 2H), 4.09 (t, J=6.1 Hz, 2H), 2.22-2.10 (m, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 169.62, 157.17, 148.61, 136.65, 135.07, 130.88, 126.27, 118.74, 117.89, 115.61, 115.46, 114.61, 81.28, 79.64, 63.94, 63.88, 30.39, 30.19. HRMS calcd. for C₁₆H₁₇FN₂O₂S [M+H]⁺ 321.1073. Found 321.1120.

Compound III-5-4 (25 mg, 0.68 mmol) was stirred in anhydrous THF (4 mL) at room temperature. 1M BH₃ in THF (3.4 mL, 3.40 mmol) was added and the reaction mixture was refluxed for 8 h. The mixture was cooled and 0.5 mL concentrated HCl (0.2 mL) was cautiously added and the solvent was removed in vacuum. 1M HCl solution (5 mL) was added then refluxed for 1 h, cooled to room temperature and pH was adjusted to 8 with a saturated solution of Na₂CO₃. The mixture was extracted with EA (20 mL×3), the organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum and purified by flash chromatography (silica gel) (methanol/DCM, 0% to 13%, vol/vol) to get product III-5-5 (12.5 mg, yield 52%) as a white solid. ¹H NMR (400 MHz, CDCl₃) δ 7.29-7.25 (m, 1H), 7.19-7.15 (m, 1H), 7.02-6.97 (m, 2H), 6.78-6.68 (m, 3H), 4.70 (t, J=5.8 Hz, 1H), 4.59 (t, J=5.8 Hz, 1H), 4.09 (t, J=6.1 Hz, 2H), 3.99 (s, 2H), 2.26-2.07 (m, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 158.18, 147.53, 143.82, 135.10, 131.30, 129.85, 124.73, 118.86, 116.79, 115.41, 114.89, 113.64, 81.46, 79.82, 63.64, 63.59, 62.74, 44.90. HRMS calcd. for C₁₆H₁₉FN₂OS [M+H]⁺ 307.1280. Found 307.1291.

Example 18 Synthesis of Compound III-5-8

A mixture of compound III-5-3 (40 mg, 0.15 mmol) and K₂CO₃ (64 mg, 0.46 mmol) was stirred in anhydrous DMF (4 mL) at 65° C. for 1.5 h. Then compound III-8 (72 mg, 0.18 mmol) was added and the mixture was stirred for another 2 h, cooled to room temperature and a saturated solution of NaCl (12 mL) was added. The mixture was extracted with EA (15 mL×3), the organic layers were combined and dried over MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Hexane, 0% to 70%, vol/vol) to get product III-5-6 (37 mg, yield 50%) as a white solid. HRMS calcd. for C₂₃H₁₈D₆N₂O₅S₂ [M+H]⁺ 479.1581. Found 479.1566.

Compound III-5-6 (37 mg, 0.08 mmol) was stirred in anhydrous THF (5 mL) at 65° C., then 1M TBAF in THF (0.23 mL, 0.23 mmol) was added. The reaction mixture was stirred for 3 h at 65° C., then the solvent was evaporated in vacuum, H₂O (8 mL) was added and the mixture was extracted with EA (15 mL×3). The organic layers were combined and dried over MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Hexane, 0% to 70%, vol/vol) to get product III-5-7 (14 mg, yield 56%) as a white solid. ¹H NMR (400 MHz, MeOD) δ 7.36 (dd, J=7.7, 1.4 Hz, 1H), 7.20-7.16 (m, 1H), 7.10-7.09 (m, 1H), 6.86-6.80 (m, 3H), 6.89-6.65 (m, 1H).

Compound III-5-7 (14 mg, 0.04 mmol) was stirred in anhydrous THF (2 mL) at room temperature, then 1M BH₃ in THF (0.43 mL, 0.43 mmol) was added. The reaction mixture was refluxed for 8 h. The mixture was cooled and 0.5 mL concentrated HCl (0.2 mL) was cautiously added and the solvent was removed in vacuum. 1M HCl solution (5 mL) was added and refluxed for 1 h, cooled to room temperature and pH was adjusted to 8 with a saturated solution of Na₂CO₃. The mixture was extracted with EA (20 mL×3). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (methanol/DCM, 0% to 13%, vol/vol) to get product III-5-8 (7 mg, yield 52%) as a white solid. ¹H NMR (400 MHz, CDCl₃) δ 7.26 (dd, J=7.7, 1.4 Hz, 1H), 7.19-7.15 (m, 1H), 7.04-6.97 (m, 2H), 6.79-6.70 (m, 3H), 4.02 (s, 2H), 3.52 (brs, 4H). ¹³C NMR (100 MHz, CDCl₃) δ 158.25, 147.50, 143.18, 135.05, 131.51, 129.89, 124.81, 118.93, 116.75, 115.49, 115.13, 113.96, 44.40. HRMS calcd. for C₁₆H₁₃D₆FN₂OS [M+H]⁺ 313.1657. Found 313.1716.

Example 19 Synthesis of Compound III-6-5

A mixture of compound III-6-1 (500 mg, 2.05 mmol), Cu (26 mg, 0.41 mmol), Cu₂O (29 mg, 0.21 mmol), 2-aminothiophenol (384 mg, 3.07 mmol) and Et₃N (2.07 g, 20.49 mmol) was stirred in 2-ethoxyethanol (8 mL) at 125° C. for 40 h. The mixture was filtered and washed with methanol (20 mL) and DCM (20 mL). The filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Hexane, 0% to 60%, vol/vol) to get product III-6-2 (350 mg, yield 59%) as a slight yellow solid. III-6-2 ¹H NMR (400 MHz, MeOD) δ 7.34 (d, J=7.7 Hz, 1H), 7.17 (dd, J=10.7, 4.7 Hz, 1H), 6.98 (d, J=2.6 Hz, 1H), 6.94-6.78 (m, 3H), 6.66 (t, J=7.5 Hz, 1H), 3.78 (s, 3H), 2.92 (s, 3H). ¹³C NMR (100 MHz, MeOD) δ 170.43, 157.99, 149.64, 136.92, 136.47, 130.38, 129.99, 125.74, 117.50, 115.99, 115.11, 112.92, 54.59, 25.32. HRMS calcd. for C₁₅H₁₆N₂O₂S [M+H]⁺ 289.1011. Found 289.1088.

Compound III-6-2 (300 mg, 1.04 mmol) was stirred in anhydrous DCM (15 mL) at 0° C. Then 1M BBr₃ in DCM (3.13 mL, 3.13 mmol) was added drop wise under nitrogen. After addition the reaction mixture was stirred at room temperature; then a saturated solution of NaHCO₃ was added and extracted with DCM (20 mL×2). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum and purified by flash chromatography (silica gel) (EA/Hexane, 0% to 70%, vol/vol) to get product III-6-3 (190 mg, yield 67%) as a colorless stick oil. ¹H NMR (400 MHz, CDCl₃) δ 7.36 (dd, J=8.0, 1.5 Hz, 1H), 7.19-7.15 (m, 1H), 6.86 (dd, J=16.0, 5.7 Hz, 2H), 6.76-6.70 (m, 2H), 6.66 (dd, J=8.6, 2.7 Hz, 1H), 6.60 (d, J=4.8 Hz, 1H), 4.41 (brs, 2H). HRMS calcd. for C₁₄H₁₄N₂O₂S [M+H]⁺ 275.0854. Found 275.0867.

A mixture of compound III-6-3 (40 mg, 0.15 mmol) and K₂CO₃ (61 mg, 0.44 mmol) was stirred in anhydrous DMF (3 mL) at 65° C. for 1.5 h. Compound 3-fluoropropyl-4-methylbenzenesulfonate (68 mg, 0.30 mmol) was added and the mixture was stirred for another 2 h, cooled to room temperature and saturated solution of NaCl (12 mL) was added. The mixture was extracted with EA (15 mL×3). The organic layers were combined and dried over MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Hexane, 0% to 80%, vol/vol) to get product III-6-4 (30 mg, yield 61%) as a colorless stick oil. HRMS calcd. for C₁₇H₁₉FN₂O₂S [M+H]⁺ 335.1230. Found 335.1185.

A mixture of compound III-6-4 (30 mg, 0.09 mmol) was stirred in anhydrous THF (4 mL) at room temperature. Then 1M BH₃ in THF (0.9 mL, 0.90 mmol) was added. The reaction mixture was refluxed for 8 h. The mixture was cooled and 0.5 mL concentrated HCl (0.5 mL) was cautiously added and the solvent was removed in vacuum. 1M HCl solution (10 mL) was added then refluxed for 1 h, cooled to room temperature and pH adjusted to 8 with a saturated solution of Na₂CO₃. The mixture was extracted with EA (20 mL×3). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (Methanol/DCM, 0% to 13%, vol/vol) to get product, III-6-5 (15 mg, yield 52%) as a colorless stick oil. ¹H NMR (400 MHz, CDCl₃) δ 7.31 (dd, J=7.7, 1.4 Hz, 1H), 7.19-7.15 (m, 1H), 6.97 (dd, J=11.8, 5.7 Hz, 2H), 6.78-6.69 (m, 3H), 4.70 (t, J=5.8 Hz, 1H), 4.57 (d, J=5.8 Hz, 1H), 4.08 (t, J=6.1 Hz, 2H), 3.90 (s, 2H), 2.50 (s, 3H), 2.21-2.11 (m, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 157.80, 147.73, 140.44, 135.43, 131.05, 129.93, 125.66, 118.69, 116.84, 115.87, 115.37, 114.08, 81.48, 79.84, 63.63, 63.58, 54.07, 36.02, 30.50, 30.30. HRMS calcd. for C₁₇H₂₁FN₂OS [M+H]⁺ 321.1437. Found 321.1451.

Example 20 Synthesis of Compound III-6-8

A mixture of compound III-5-5 (20 mg, 0.07 mmol) and Et₃N (33 mg, 0.33 mmol) was stirred in anhydrous DCM (7 mL) at 0° C. (Boc)₂O (30 mg, 0.14 mmol) was added drop wise. After addition the reaction was stirred at room temperature for 3 h. Then H₂O (30 mL) was added. The mixture was extracted with DCM (10 mL×2), the organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Hexane, 0% to 70%, vol/vol) to get product III-6-6 (17 mg, 64%) as a colorless oil. ¹H NMR (400 MHz, CDCl₃) δ 7.24 (d, J=7.7 Hz, 1H), 7.19-7.13 (m, 1H), 7.03 (d, J=8.6 Hz, 1H), 6.96 (d, J=2.4 Hz, 1H), 6.77-6.70 (m, 3H), 4.96 (s, 1H), 4.70 (t, J=5.8 Hz, 1H), 4.58 (t, J=5.8 Hz, 1H), 4.44 (d, J=5.6 Hz, 2H), 4.22 (s, 2H), 4.08 (t, J=6.1 Hz, 2H), 2.24-2.04 (m, 2H), 1.47 (s, 9H). ¹³C NMR (100 MHz, CDCl₃) 158.16, 155.79, 147.36, 139.82, 134.90, 131.60, 129.84, 118.96, 115.48, 115.36, 114.30, 81.43, 79.79, 77.32, 63.66, 63.60, 42.97, 30.45, 30.25, 28.41. HRMS calcd. for C₂₁H₂₇FN₂O₃S [M+H]⁺ 407.1805. Found 407.1763.

Compound III-6-6 (17 mg, 0.04 mmol) was stirred in anhydrous DMF (2 mL) at 0° C., then 60% NaH (3.3 mg, 0.08 mmol) was added slowly. After addition, the reaction was stirred at 0° C. for 30 min. Deuterated iodomethane (9 mg, 0.06 mmol) was added and stirred for another 1 h at 0° C. Saturated solution of NaCl (15 mL) was added and the mixture was extracted with EA (20 mL×2). The organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Hexane, 0% to 50%, vol/vol) to get product III-6-7 (13 mg, 73%) as a white solid. ¹H NMR (400 MHz, CDCl₃) δ 7.18-7.14 (m, 2H), 7.04-6.94 (m, 1H), 6.77-6.70 (m, 4H), 4.70 (t, J=5.8 Hz, 1H), 4.58 (t, J=5.8 Hz, 1H), 4.19 (brs, 2H), 4.07 (t, J=6.1 Hz, 2H), 2.22-2.10 (m, 2H), 1.52-1.46 (m, 9H). HRMS calcd. for C₂₂H₂₆D₃FN₂O₃S [M+H]⁺424.2149. Found 424.2158.

Compound III-6-7 (13 mg, 0.03 mmol) was stirred in CF₃COOH (3 mL) at room temperature overnight, then the solvent was evaporated in vacuum. The pH was adjusted to 8 with a saturated solution of Na₂CO₃ The mixture was extracted with EA (10 mL×3), the organic layers were combined and dried over anhydrous MgSO₄, filtered and the filtrate was evaporated in vacuum, purified by flash chromatography (silica gel) (EA/Methanol, 0% to 10%, vol/vol) to get product III-6-8 (5 mg, 50%) as a colorless oil. ¹H NMR (400 MHz, CDCl₃) δ 7.29-7.27 (m, 1H), 7.20-7.15 (m, 1H), 7.04-7.01 (m, 2H), 6.77-6.71 (m, 3H), 4.69 (t, J=5.8 Hz, 1H), 4.57 (t, J=5.8 Hz, 1H), 4.08 (t, J=6.1 Hz, 2H), 3.99 (s, 2H), 2.23-2.04 (m, 2H). ¹³C NMR (100 MHz, CDCl₃) δ 157.99, 147.71, 137.89, 135.36, 131.44, 130.08, 126.01, 118.86, 116.50, 116.27, 115.55, 114.97, 81.43, 79.79, 63.70, 63.65, 52.86, 30.44, 30.24. HRMS calcd. for C₁₇H₁₈D₃FN₂OS [M+H]⁺ 324.1625. Found 324.1628.

Example 21 Radiolabeling of ¹⁸F-III-3 (¹⁸F—FPBM-D12)

Preparation of ¹⁸F-III-3 (¹⁸F—FPBM-D₁₂) by radiolabeling was accomplished by the following steps. ¹⁸F fluoride was loaded on an activated QMA light cartridge and eluted with 0.7 mL K₂₂₂/K₂CO₃ solution (40 mg K₂CO₃, 220 mg K₂₂₂, 3.6 mL water, 18.4 mL ACN) into a conical vial. The solution was dried under a flow of argon at 80° C. and azeotropically dried twice with 1 mL acetonitrile. 2 mg precursor was dissolved in 0.5 ml acetonitrile (anhydrous) and added to dried ¹⁸F F⁻/K₂₂₂/K₂CO₃ complex. The reaction mixture, containing III-3-1, was heated for 15 min at 80° C. The resulting reaction mixture was cooled to room temperature and added to 8 mL water. The mixture was loaded onto an Oasis HLB (3 cc) cartridge. Cartridge was eluted and washed twice with 3 mL water. The desired ¹⁸F-III-3 was eluted with 1 ml acetonitrile (yield: 53%, RCP ˜99% HPLC (Supelco Ascentis 150×4.6 mm, ACN/10 mM ammonium format buffer (AFB) 50/50, 1 mL/min). 1 mL of water was added to this solution and injected onto prep HPLC (Phenomenx Gemini 250×10 mm, ACN/water 60/40, 4 mL/min). The eluent of the desired ¹⁸F-III-3 was collected (14.5 mCi, retention time 21-22 min). The solution was mixed with 30 mL water and added onto an Oasis HLB 3 cc. The activity was eluted with 1 mL 100% ethanol (12.2 mCi). The solution was concentrated to about 200 μL volume and diluted with 1.8 mL buffer. Radio profile on HPLC (HPLC: Supelco Ascentis 150×4.6 mm, ACN/10 mM AFB 50/50, 1 mL/min) showed single peak at 4 minutes for ¹⁸F-III-3 (¹⁸F—FPBM-D12), RCY 32% (dc): RCP: 99%; SA˜1700 Ci/mmol (determined at 280 nm). The retention time corresponded to cold III-3 confirming the chemical identity.

Example 22 In Vitro Binding Assays

The membrane homogenates of serotonin transporters (LLC-SERT, which were expressed in a common parental cell line LLC-PK1) were prepared and used for the binding assays. Competitive binding assays were performed in a final volume of 0.25 mL. Aliquots of membrane suspensions were mixed with 50 mM Tris-HCl, pH 7.4, 120 mM NaCl and 0.1% bovine serum albumin, 0.2 nM [¹²⁵I]IDAM, and 8-10 concentrations (10⁻¹³ to 10⁻⁷M) of competing drugs. Nonspecific binding was defined with 10 μM citalopram. Incubation was carried out for 60 min at room temperature and the bound ligand was collected on glass fiber filters presoaked with 1% polyethylenimine (SIGMA, St. Louis, Mo.) and counted in a gamma counter (Wizard², Perkin Elmer). Data were analyzed using the nonlinear least-square curve fitting program LIGAND to determine IC₅₀ and Ki was calculated by Cheng-Prusoff equation using 0.2 nM as Kd of [¹²⁵I]IDAM.

TABLE 3a A ring halogen (X) substitution on SERT binding affinity. X Ki (nM)

H F Cl Br III-1-1 III-4-19 III-4-17 III-4-18 1.21 ± 0.15 0.22 ± 0.06 0.03 ± 0.01  0.02 ± 0.002

H F Cl Br I III-4-2 III-4-27 III-4-25 III-4-26 III-4-28 0.14 ± 0.06 0.024 ± 0.004 0.009 ± 0.004 0.021 ± 0.003 0.008 ± 0.003 Deuterated

The binding affinity of deuterated agents in this series showed very high binding affinity. Adding fluoropropyl-D6 group showed comparable binding affinity.

TABLE 3b The effect of N-methyl substitution groups on SERT binding affinity. Ki (nM) Deuterated Ki (nM)

III-1 (FPBM) 0.052 ± 0.007

III-4-2 0.14 ± 0.06

III-6-5 5.26 ± 0.66

III-6-8 3.05 ± 0.81

III-5-5 39.3 ± 11.9

III-5-8 44.9 ± 2.5 

In this series of agents the binding affinity is dependent on the N,N-dimehtyl substitution with the di-substituted compound with or without deuterium show the highest binding affinity.

TABLE 3c Hydrogen vs Deuterium substitution on SERT binding affinity. Ki (nM) Deuterated Ki (nM)

III-1-1 1.21 ± 0.15

III-2-4 2.02 ± 0.54

III-1 (FPBM) 0.052 ± 0.007

III-2 0.032 ± 0.013

III-3 (FPBM- D12) 0.086 ± 0.029

0.022 ± 0.016

III-4-27 0.024 ± 0.004

III-5-5 39.3 ± 11.9

III-5-8 44.9 ± 2.5 

III-6-5 5.26 ± 0.66

III-6-8 3.05 ± 0.81

Binding affinity study shows that the deuterated agents all display comparable binding affinity towards SERT binding sites when compared to the corresponding non-deuterated agents. The novel deuterated agents can be useful for binding to SERT binding sites.

Example 23 Biodistribution in Rats

Three rats per group were used for each biodistribution study. While under isoflurane anesthesia, 0.2 mL of a saline solution containing 20 μCi of radioactive tracer was injected into the femoral vein. The rats were sacrificed at the time indicated by cardiac excision while under isoflurane anesthesia. Organs of interest were removed and weighed, and the radioactivity was counted. The percent dose per organ was calculated by comparing the tissue counts to counts of 1% of the initial dose (100 times diluted aliquots of the injected material) measured at the same time. Regional brain distribution in rats was measured after an iv injection of the radioactive tracer. Samples from different brain regions [cortex, striatum, hippocampus, cerebellum and hypothalamus] were dissected, weighed and counted. The percentage dose/g of each sample was calculated by comparing sample counts with the counts of the diluted initial dose described above. The ratio was calculated by dividing the percentage dose/g of each region by that of the cerebellum. The cerebellum was used as the reference region for calculating the ratio of target to non-target binding, because only a trace amount of SERT is present in the cerebellum.

TABLE 3d Biodistribution of ¹⁸F-III-3 (¹⁸F-FPBM-D12) in normal rats at different time points after an i.v. injection % Dose/g (Avg ± SD of n = 3). 2 min 30 min 60 min 120 min Blood 0.25 ± 0.04 0.16 ± 0.03 0.10 ± 0.02 0.06 ± 0.00 Heart 1.19 ± 0.18 0.18 ± 0.02 0.09 ± 0.01 0.05 ± 0.01 Muscle 0.14 ± 0.02 0.09 ± 0.02 0.07 ± 0.01 0.03 ± 0.01 Lung 9.56 ± 2.29 1.86 ± 0.42 0.850.11 0.450.10 Kidney 3.02 ± 0.16 1.79 ± 0.38 1.29 ± 0.29 0.83 ± 0.39 Spleen 1.48 ± 0.31 0.88 ± 0.05 0.46 ± 0.10 0.21 ± 0.04 Pancreas 1.13 ± 0.02 0.27 ± 0.06 0.19 ± 0.02 0.13 ± 0.07 Liver 0.74 ± 0.16 0.30 ± 0.05 0.22 ± 0.02 0.16 ± 0.01 Skin 0.22 ± 0.04 0.19 ± 0.03 0.16 ± 0.01 0.10 ± 0.02 Bone 0.35 ± 0.06 0.19 ± 0.01 0.16 ± 0.02 0.13 ± 0.01 Brain 1.09 ± 0.06 0.81 ± 0.04 0.54 ± 0.05 0.31 ± 0.03 Region to Cerebellum Ratio ¹⁸F-III-3 (¹⁸F-FPBM-D12) 2 min 30 min 60 min 120 min Hypothalamus 1.17 ± 0.21 2.99 ± 0.46 5.32 ± 0.45 7.55 ± 0.82 Cerebellum 1.00 ± 0.00 1.00 ± 0.00 1.00 ± 0.00 1.00 ± 0.00 Hippocampus 0.97 ± 0.13 2.04 ± 0.27 3.45 ± 0.42 3.85 ± 0.28 Cortex 1.44 ± 0.27 1.81 ± 0.30 2.68 ± 0.35 2.67 ± 0.50 Striatum 1.15 ± 0.18 2.43 ± 0.38 3.96 ± 0.62 4.69 ± 1.26 Remainder 1.21 ± 0.13 2.42 ± 0.13 3.77 ± 0.43 4.74 ± 0.71 Region to Cerebellum Ratio ¹⁸F-III-1 (¹⁸F-FPBM) (Reported previously, Wang, J. Nucl. Med. 2009, 50:1509-17) Organ 2 min 30 min 60 min 120 min Hypothalamus 1.14 ± 0.16 3.50 ± 0.67 4.69 ± 1.76 7.67 ± 2.60 Cerebellum 1.00 ± 0.15 1.00 ± 0.19 1.00 ± 0.46 1.00 ± 0.33 Hippocampus 0.88 ± 0.11 2.26 ± 0.44 2.82 ± 1.06 3.87 ± 1.00 Cortex 1.03 ± 0.13 2.87 ± 0.64 4.26 ± 1.58 4.53 ± 1.33 Striatum 0.90 ± 0.10 2.58 ± 0.59 3.19 ± 1.23 4.67 ± 1.51 Remainder 0.98 ± 0.14 2.54 ± 0.40 3.11 ± 1.22 4.49 ± 1.29

The biodistribution study in rats after an i.v. injection of ¹⁸F-III-3 (¹⁸F—FPBM-D12) showed that the new deuterated agent penetrated the blood-brain-barrier and localized in the regions, where the concentration of serotonin transporter binding sites are high, i.e., hypothalamus and striatum regions (Table 3d). The regional distribution of deuterated, ¹⁸F-III-3 (¹⁸F—FPBM-D12), in the brain is comparable to that of the non-deuterated ¹⁸F-III-1 (¹⁸F—FPBM), reported previously.

The novel new deuterated compound, ¹⁸F-III-3 (¹⁸F—FPBM-D12), can be useful for imaging patients before and after taking serotonin reuptake inhibitors (SSRIs) for monitoring the drug effects. The “cold” agent as described above may also be useful for specific therapy where blocking serotonin uptake is indicated.

While certain embodiments have been illustrated and described, it should be understood that changes and modifications can be made therein in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the following claims.

The present disclosure is not to be limited in terms of the particular embodiments described in this application. Modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and compositions within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds compositions or biological systems, which can of course vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

All publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.

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What is claimed is:
 1. A compound having Formula II-B:

or a pharmaceutically acceptable salt thereof, wherein: R² is CD₃; X is ¹⁸F or F; Y is —[O(CR^(a)R^(b))₂]_(m)—, wherein R^(a) and R^(b) are each independently hydrogen or deuterium atoms; m is 3; and A¹ is N or CH.
 2. The compound of claim 1, or a pharmaceutically acceptable salt thereof, wherein Y is —[O(CR^(s)R^(b))₂]₃—.
 3. The compound of claim 1, having Formula II-C:

or a pharmaceutically acceptable salt thereof, wherein: A¹ is N or CH; and X is ¹⁸F or F.
 4. The compound of claim 3, or a pharmaceutically acceptable salt thereof, wherein A¹ is N and X is ¹⁸F.
 5. The compound of claim 2, or a pharmaceutically acceptable salt thereof, wherein A¹ is N and X is ¹⁸F.
 6. A pharmaceutical composition comprising the compound of claim 1, or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.
 7. A method of in vivo imaging, comprising administering an effective amount of the compound of claim 1 wherein X is ¹⁸F, or a pharmaceutically acceptable salt thereof to a subject; and scanning said subject to detect the pattern of positron emission tomography, whereby an image is generated from the pattern of positron emission.
 8. A pharmaceutical composition comprising the compound of claim 4, or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.
 9. A method of in vivo imaging, comprising administering an effective amount of the compound of claim 4 or a pharmaceutically acceptable salt thereof to a subject; and scanning said subject to detect the pattern of positron emission tomography, whereby an image is generated from the pattern of positron emission.
 10. A pharmaceutical composition comprising the compound of claim 5, or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.
 11. A method of in vivo imaging, comprising administering an effective amount of the compound of claim 5 or a pharmaceutically acceptable salt thereof to a subject; and scanning said subject to detect the pattern of positron emission tomography, whereby an image is generated from the pattern of positron emission.
 12. The compound of claim 3, or a pharmaceutically acceptable salt thereof, wherein A¹ is N and X is F.
 13. The compound of claim 2, or a pharmaceutically acceptable salt thereof, wherein A¹ is N and X is F. 